More RP1 PIO DMA tweaks #4367

Job	Run time
build (bcm2711_rt, arm64, bcm2711_rt_defconfig, kernel8_rt)	22m 0s
build (bcm2711, arm64, bcm2711_defconfig, kernel8)	21m 57s
build (arm64, arm64, defconfig, kernel8)	18m 37s
build (bcm2709, arm, bcm2709_defconfig, kernel7)	17m 35s
build (bcm2835, arm, bcm2835_defconfig, kernel)	5m 55s
build (bcmrpi, arm, bcmrpi_defconfig, kernel)	18m 1s
build (bcm2712, arm64, bcm2712_defconfig, kernel_2712)	22m 26s
	2h 6m 31s

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