arm64/Kconfig: Don't set DMA_BOUNCE_UNALIGNED_KMALLOC

If enabled, DMA_BOUNCE_UNALIGNED_KMALLOC causes the swiotlb buffers
(64MB, by default) to be allocated, even on systems where the DMA
controller can reach all of RAM. This is a huge amount of RAM to
waste on a device with only 512MB to start with, such as the Zero 2 W.

See: #5975

Signed-off-by: Phil Elwell <[email protected]>

Author: pelwell

arch/arm64/Kconfig

@@ -137,7 +137,8 @@ config ARM64
 	select CRC32
 	select DCACHE_WORD_ACCESS
 	select DYNAMIC_FTRACE if FUNCTION_TRACER
-	select DMA_BOUNCE_UNALIGNED_KMALLOC
+	# Disable this to save 64MB when DMA controllers can reach all of RAM
+	# select DMA_BOUNCE_UNALIGNED_KMALLOC
 	select DMA_DIRECT_REMAP
 	select EDAC_SUPPORT
 	select FRAME_POINTER