mm: remove the BOUNCE config option

Commit eeadd68e2a5f ("block: remove bounce buffering support") remove
block/bounce.c but left the BOUNCE config option.  Now this option has no
users, so remove it.

Link: https://lkml.kernel.org/r/20251013095620.1111061-1-chenhuacai@loongson.cn
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>
Acked-by: David Hildenbrand <david@redhat.com>
Acked-by: Jens Axboe <axboe@kernel.dk>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Anshuman Khandual <anshuman.khandual@arm.com>
Cc: Hannes Reinecke <hare@suse.de>
Cc: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Cc: John Garry <john.g.garry@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: maoxiaochuan <maoxiaochuan@loongson.cn>

mm/Kconfig

@@ -711,15 +711,6 @@ config PCP_BATCH_SCALE_MAX
 config PHYS_ADDR_T_64BIT
 	def_bool 64BIT
 
-config BOUNCE
-	bool "Enable bounce buffers"
-	default y
-	depends on BLOCK && MMU && HIGHMEM
-	help
-	  Enable bounce buffers for devices that cannot access the full range of
-	  memory available to the CPU. Enabled by default when HIGHMEM is
-	  selected, but you may say n to override this.
-
 config MMU_NOTIFIER
 	bool
 	select INTERVAL_TREE