Documentation: xfs: consolidate XFS docs into its own subdirectory

XFS docs are currently in upper-level Documentation/filesystems.
Although these are currently 4 docs, they are already outstanding as
a group and can be moved to its own subdirectory.

Consolidate them into Documentation/filesystems/xfs/.

Signed-off-by: Bagas Sanjaya <[e-mail]>
Reviewed-by: Bill O'Donnell <[e-mail]>
Reviewed-by: "Darrick J. Wong" <[e-mail]>
Signed-off-by: Chandan Babu R <[e-mail]>

Documentation/filesystems/index.rst

···
    udf
    virtiofs
    vfat
-   xfs-delayed-logging-design
-   xfs-maintainer-entry-profile
-   xfs-self-describing-metadata
-   xfs-online-fsck-design
+   xfs/index
    zonefs

Documentation/filesystems/xfs-online-fsck-design.rst Documentation/filesystems/xfs/xfs-online-fsck-design.rst

···
 between metadata structures.
 
 For more information, please see the documentation for
-Documentation/filesystems/xfs-self-describing-metadata.rst
+Documentation/filesystems/xfs/xfs-self-describing-metadata.rst
 
 Reverse Mapping
 ---------------

Documentation/filesystems/xfs/index.rst

···
+.. SPDX-License-Identifier: GPL-2.0
+
+============================
+XFS Filesystem Documentation
+============================
+
+.. toctree::
+   :maxdepth: 2
+   :numbered:
+
+   xfs-delayed-logging-design
+   xfs-maintainer-entry-profile
+   xfs-self-describing-metadata
+   xfs-online-fsck-design

Documentation/maintainer/maintainer-entry-profile.rst

···
    ../driver-api/media/maintainer-entry-profile
    ../driver-api/vfio-pci-device-specific-driver-acceptance
    ../nvme/feature-and-quirk-policy
-   ../filesystems/xfs-maintainer-entry-profile
+   ../filesystems/xfs/xfs-maintainer-entry-profile

MAINTAINERS

···
 W:	http://xfs.org/
 C:	irc://irc.oftc.net/xfs
 T:	git git://git.kernel.org/pub/scm/fs/xfs/xfs-linux.git
-P:	Documentation/filesystems/xfs-maintainer-entry-profile.rst
+P:	Documentation/filesystems/xfs/xfs-maintainer-entry-profile.rst
 F:	Documentation/ABI/testing/sysfs-fs-xfs
 F:	Documentation/admin-guide/xfs.rst
-F:	Documentation/filesystems/xfs-*
+F:	Documentation/filesystems/xfs/*
 F:	fs/xfs/
 F:	include/uapi/linux/dqblk_xfs.h
 F:	include/uapi/linux/fsmap.h