HAL_ChibiOS: avoid an issue with DCache init on H743

this fixes an issue found by Andy Piper where the H743 bootloader gets
a hard fault in the DCache enable code when SRAM1 is primary memory.

This is the simplest fix I could think of, and avoids the problem by
making DTCM the first segment in the bootloader.

Note that we can't use DTCM as first segment for main firmware since
we went to double precision EKF as the static variables don't fit

libraries/AP_HAL_ChibiOS/hwdef/scripts/STM32H743xx.py

@@ -34,6 +34,18 @@
         (0x38000000,  64, 1), # SRAM4.
     ],
 
+    # avoid a problem in the bootloader by making DTCM first. The DCache init
+    # when using SRAM1 as primary memory gets a hard fault in bootloader
+    # we can't use DTCM first for main firmware as some builds overflow the first segment
+    'RAM_MAP_BOOTLOADER' : [
+        (0x20000000, 128, 2), # DTCM, tightly coupled, no DMA, fast
+        (0x30000000, 256, 0), # SRAM1, SRAM2
+        (0x24000000, 512, 4), # AXI SRAM. Use this for SDMMC IDMA ops
+        (0x00000400,  63, 2), # ITCM (first 1k removed, to keep address 0 unused)
+        (0x30040000,  32, 0), # SRAM3.
+        (0x38000000,  64, 1), # SRAM4.
+    ],
+
     'EXPECTED_CLOCK' : 400000000,
 
     # this MCU has M7 instructions and hardware double precision

libraries/AP_HAL_ChibiOS/hwdef/scripts/chibios_hwdef.py

@@ -671,6 +671,15 @@ def has_sdcard_spi():
     return False
 
 
+def get_ram_map():
+    '''get RAM_MAP. May be different for bootloader'''
+    if args.bootloader:
+        ram_map = get_mcu_config('RAM_MAP_BOOTLOADER', False)
+        if ram_map is not None:
+            return ram_map
+    return get_mcu_config('RAM_MAP', True)
+
+
 def write_mcu_config(f):
     '''write MCU config defines'''
     f.write('// MCU type (ChibiOS define)\n')
@@ -788,7 +797,7 @@ def write_mcu_config(f):
         f.write('#define APP_START_OFFSET_KB %u\n' % get_config('APP_START_OFFSET_KB', default=0, type=int))
     f.write('\n')
 
-    ram_map = get_mcu_config('RAM_MAP', True)
+    ram_map = get_ram_map()
     f.write('// memory regions\n')
     regions = []
     total_memory = 0
@@ -930,7 +939,7 @@ def write_ldscript(fname):
     flash_reserve_end = get_config('FLASH_RESERVE_END_KB', default=0, type=int)
 
     # ram layout
-    ram_map = get_mcu_config('RAM_MAP', True)
+    ram_map = get_ram_map()
     instruction_ram = get_mcu_config('INSTRUCTION_RAM', False)
 
     flash_base = 0x08000000 + flash_reserve_start * 1024