xfs: fix Kconfig asking about XFS_SUPPORT_V4 when XFS_FS=n

Pavel Machek complained that the question about supporting deprecated
XFS v4 comes up even when XFS is disabled.  This clearly makes no sense,
so fix Kconfig.
Reported-by: Pavel Machek <pavel@ucw.cz>
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: Eric Sandeen <sandeen@redhat.com>

fs/xfs/Kconfig

@@ -24,6 +24,7 @@ config XFS_FS
 
 config XFS_SUPPORT_V4
 	bool "Support deprecated V4 (crc=0) format"
+	depends on XFS_FS
 	default y
 	help
 	  The V4 filesystem format lacks certain features that are supported