fs/Kconfig: Fix compile error for romfs

There are some compile errors reported by kernel test robot:

arm-linux-gnueabi-ld: fs/romfs/storage.o: in function `romfs_dev_read':
storage.c:(.text+0x64): undefined reference to `__brelse'
arm-linux-gnueabi-ld: storage.c:(.text+0x9c): undefined reference to `__bread_gfp'
arm-linux-gnueabi-ld: fs/romfs/storage.o: in function `romfs_dev_strnlen':
storage.c:(.text+0x128): undefined reference to `__brelse'
arm-linux-gnueabi-ld: storage.c:(.text+0x16c): undefined reference to `__bread_gfp'
arm-linux-gnueabi-ld: fs/romfs/storage.o: in function `romfs_dev_strcmp':
storage.c:(.text+0x22c): undefined reference to `__bread_gfp'
arm-linux-gnueabi-ld: storage.c:(.text+0x27c): undefined reference to `__brelse'
arm-linux-gnueabi-ld: storage.c:(.text+0x2a8): undefined reference to `__bread_gfp'
arm-linux-gnueabi-ld: storage.c:(.text+0x2bc): undefined reference to `__brelse'
arm-linux-gnueabi-ld: storage.c:(.text+0x2d4): undefined reference to `__brelse'
arm-linux-gnueabi-ld: storage.c:(.text+0x2f4): undefined reference to `__brelse'
arm-linux-gnueabi-ld: storage.c:(.text+0x304): undefined reference to `__brelse'

The reason for the problem is that the commit
"925c86a1" ("fs: add CONFIG_BUFFER_HEAD") has added a new config
"CONFIG_BUFFER_HEAD" that controls building the buffer_head code, and
romfs needs to use the buffer_head API, but no corresponding config has
beed added. Select the config "CONFIG_BUFFER_HEAD" in romfs Kconfig to
resolve the problem.

Fixes: 925c86a1 ("fs: add CONFIG_BUFFER_HEAD")
Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202308031810.pQzGmR1v-lkp@intel.com/Reviewed-by: Luis Chamberlain <mcgrof@kernel.org>
Tested-by: Li Zetao <lizetao1@huawei.com>
Signed-off-by: Li Zetao <lizetao1@huawei.com>
[axboe: fold in Christoph's incremental]
Signed-off-by: Jens Axboe <axboe@kernel.dk>

fs/romfs/Kconfig

@@ -57,6 +57,7 @@ endchoice
 config ROMFS_ON_BLOCK
 	bool
 	default y if ROMFS_BACKED_BY_BLOCK || ROMFS_BACKED_BY_BOTH
+	select BUFFER_HEAD
 
 config ROMFS_ON_MTD
 	bool