xfs: Default XFS_RT to Y if CONFIG_BLK_DEV_ZONED is enabled

XFS support for zoned block devices requires the realtime subvolume
support (XFS_RT) to be enabled. Change the default configuration value
of XFS_RT from N to CONFIG_BLK_DEV_ZONED to align with this requirement.
This change still allows the user to disable XFS_RT if this feature is
not desired for the user use case.

Suggested-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Damien Le Moal <dlemoal@kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Carlos Maiolino <cmaiolino@redhat.com>
Signed-off-by: Carlos Maiolino <cem@kernel.org>