xfs: small fixes for 5.12

Here's a handful of bug fixes for 5.12.  The first one fixes a bug in
quota accounting on idmapped mounts; the second avoids a buffer deadlock
in bulkstat/inumbers if the inobt is corrupt; and the third fixes a
mount hang if mount fails after creating (or otherwise dirtying) the
quota inodes.

v2: remove unnecessary freeze protection from fsmap, refactor shared
    parts of unmount code, tweaks to the itable deadlock detection