dm: make EBS depend on !HIGHMEM

__ebs_rw_bvec use page_address on the submitted bios data, and thus
can't deal with highmem.  Disable the target on highmem configs.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Link: https://lore.kernel.org/r/20210804095634.460779-4-hch@lst.de
Signed-off-by: Jens Axboe <axboe@kernel.dk>

drivers/md/Kconfig

@@ -342,7 +342,7 @@ config DM_WRITECACHE
 
 config DM_EBS
 	tristate "Emulated block size target (EXPERIMENTAL)"
-	depends on BLK_DEV_DM
+	depends on BLK_DEV_DM && !HIGHMEM
 	select DM_BUFIO
 	help
 	  dm-ebs emulates smaller logical block size on backing devices