Add support for gpu_direct in ffmepg ffmpeg plugin

[DawidWesierski4]

Add support for gpu_direct in ffmepg ffmpeg plugin
Introduces suport for experimental MTL_GPU_DIRECT
feature to enhance the performance of the FFmpeg
ST20p plugin by enabling direct GPU memory access.

Update ffmpeg README.md
-- include build instructions and description of
the feature

Modify build_ffmpeg_plugin.sh
-- Add support for building with GPU_DIRECT

[DawidWesierski4]

few basic tests done

building running on default / GPU enabled mode seems to work fine

[in#0/mtl_st20p @ 0x56812e879dc0] Input file #0 (0):
[in#0/mtl_st20p @ 0x56812e879dc0] Input stream #0:0 (video): 250 packets read (2073600000 bytes); 250 frames decoded; 0 decode errors;
[in#0/mtl_st20p @ 0x56812e879dc0] Total: 250 packets (2073600000 bytes) demuxed
MTL: 2024-09-10 12:03:51, st20p_rx_free(0), start
MTL: 2024-09-10 12:03:51, st20_rx_free(0,0), start
MTL: 2024-09-10 12:03:51, RX_VIDEO_SESSION(0,0:st20p_rx_ffmpeg): fps 1.824542 frames 2 pkts 6367
MTL: 2024-09-10 12:03:51, RX_VIDEO_SESSION(0,0): throughput 6.739931 Mb/s, cpu busy 0.300052
MTL: 2024-09-10 12:03:51, RX_VIDEO_SESSION(0,0): succ burst max 5, avg 1.000629
MTL: 2024-09-10 12:03:51, mt_dev_put_rx_queue(0), q 1
MTL: 2024-09-10 12:03:51, sch_free_quota(0), quota 1620 total now 0
MTL: 2024-09-10 12:03:51, st20_rx_free, succ on sch 0 session 0
MTL: 2024-09-10 12:03:51, st20p_rx_free(0), succ
[mtl_st20p @ 0x56812e879f40] mtl_instance_put, handle 0x3200b80f00 ref cnt 0
[mtl_st20p @ 0x56812e879f40] mtl_instance_put, ref cnt reach zero, uninit mtl device
MTL: 2024-09-10 12:03:51, sch_tasklet_func(0), end with 1 tasklets
MTL: 2024-09-10 12:03:51, mt_sch_put_lcore, succ on manager lcore 36 for lib_sch
MTL: 2024-09-10 12:03:51, sch_stop(0), succ
MTL: 2024-09-10 12:03:51, mt_sch_stop_all, succ
MTL: 2024-09-10 12:03:51, _mt_stop, succ
MTL: 2024-09-10 12:03:51, admin_thread, stop
MTL: 2024-09-10 12:03:51, cni_traffic_thread, stop
MTL: 2024-09-10 12:03:51, mt_dev_put_rx_queue(0), q 0
MTL: 2024-09-10 12:03:51, mt_cni_uinit, succ
MTL: 2024-09-10 12:03:51, sch_free_quota(0), quota 0 total now 0
MTL: 2024-09-10 12:03:51, mt_sch_put(0), ref_cnt now zero
MTL: 2024-09-10 12:03:51, Warn: sch_stop(0), not started
MTL: 2024-09-10 12:03:51, mtl_sch_unregister_tasklet(0), tasklet rvs_pkt_rx(0) unregistered
MTL: 2024-09-10 12:03:51, rvs_mgr_uinit(0), succ
MTL: 2024-09-10 12:03:51, sch_free(0), start to free sch: sch_0
MTL: 2024-09-10 12:03:51, mt_dpdk_flush_tx_queue(0), queue 0 burst_pkts 1024
MTL: 2024-09-10 12:03:51, mt_dev_put_tx_queue(0), q 0
MTL: 2024-09-10 12:03:51, dev_stop_port(0), succ
MTL: 2024-09-10 12:03:51, mt_dev_free, succ
MTL: 2024-09-10 12:03:51, mt_main_free, succ
MTL: 2024-09-10 12:03:51, mt_mempool_free, free mempool R_P0Q0_MBUF_1
MTL: 2024-09-10 12:03:51, mt_mempool_free, free mempool R_P0Q1_MBUF_2
MTL: 2024-09-10 12:03:51, mt_mempool_free, free mempool R_P0Q2_MBUF_3
MTL: 2024-09-10 12:03:51, mt_mempool_free, free mempool R_P0Q3_MBUF_4
MTL: 2024-09-10 12:03:51, mt_mempool_free, free mempool R_P0Q4_MBUF_5
MTL: 2024-09-10 12:03:51, mt_mempool_free, free mempool R_P0Q5_MBUF_6
MTL: 2024-09-10 12:03:51, mt_mempool_free, free mempool R_P0Q6_MBUF_7
MTL: 2024-09-10 12:03:51, mt_mempool_free, free mempool R_P0Q7_MBUF_8
MTL: 2024-09-10 12:03:51, mt_mempool_free, free mempool R_P0Q8_MBUF_9
MTL: 2024-09-10 12:03:51, mt_mempool_free, free mempool T_P0_SYS_0
MTL: 2024-09-10 12:03:51, dev_close_port(0), succ
MTL: 2024-09-10 12:03:51, stat_thread, stop
MTL: 2024-09-10 12:03:51, mt_dev_uinit, succ
MTL: 2024-09-10 12:03:51, mtl_uninit, succ
[mtl_st20p @ 0x56812e879f40] mtl_st20p_read_close(0), frame_counter 250

on GPU enabled mode no obvious errors / framedrops

[DawidWesierski4]

also

MTL: 2024-09-10 12:48:09, rv_alloc_frames rv_framebuffer_in_gpu_direct_vram

frames are allocated in vram

[tszumski]

There is no information on how to get the appropriate driver and device index

[DawidWesierski4]

There is no information on how to get the appropriate driver and device index

there is no easy way to find this information tbh outside zero level library

Added it as a log for the user to see
If initialization fails there will be a clear log
Driver: 0: Device: 0:

-- fail to initialize

[soopel]

Code review completed