docs: filesystems: convert gfs2-glocks.txt to ReST

- Add a SPDX header;
- Adjust document and section titles;
- Some whitespace fixes and new line breaks;
- Add table markups;
- Use notes markups;
- Add it to filesystems/index.rst.
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com>

Documentation/filesystems/index.rst

@@ -69,6 +69,7 @@ Documentation for filesystem implementations.
    f2fs
    gfs2
    gfs2-uevents
+   gfs2-glocks
    hfs
    hfsplus
    hpfs

MAINTAINERS

@@ -7179,7 +7179,7 @@ L:	cluster-devel@redhat.com
 S:	Supported
 W:	http://sources.redhat.com/cluster/
 T:	git git://git.kernel.org/pub/scm/linux/kernel/git/gfs2/linux-gfs2.git
-F:	Documentation/filesystems/gfs2*.txt
+F:	Documentation/filesystems/gfs2*
 F:	fs/gfs2/
 F:	include/uapi/linux/gfs2_ondisk.h