Make board_crashdump.c arch agnostic and move to common

src/drivers/boards/px4fmu-v2/CMakeLists.txt

@@ -34,7 +34,7 @@ px4_add_module(
 	MODULE drivers__boards__px4fmu-v2
 	COMPILE_FLAGS
 	SRCS
-		../common/stm32/board_crashdump.c
+		../common/board_crashdump.c
 		../common/board_dma_alloc.c
 		px4fmu_can.c
 		px4fmu2_init.c

src/drivers/boards/px4fmu-v2/px4fmu2_init.c

@@ -477,10 +477,3 @@ __EXPORT int board_app_initialize(uintptr_t arg)
 
 	return OK;
 }
-
-static void copy_reverse(stack_word_t *dest, stack_word_t *src, int size)
-{
-	while (size--) {
-		*dest++ = *src--;
-	}
-}