gfs2: Add some flags missing from glock output

Before this patch, three flags were not represented in the glock output.
This patch adds them in:

c - GLF_INODE_CREATING
P - GLF_PENDING_DELETE
x - GLF_FREEING (both f and F are already used)

Signed-off-by: Bob Peterson <rpeterso@redhat.com>
Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com>