convert XFS perag lookup to xarrays v2

[Christoph Hellwig <hch@lst.de>]

Hi all,

for a project with the pending RT group code in XFS that reuses the basic
perag concepts I'd much prefer to use xarrays over the old radix tree for
nicer iteration semantics.

This series converts the perag code to xarrays to keep them in sync and
throws in the use of kfree_rcu_mightsleep in the same area.

Changes since v1:
 - use xa_insert instead of reinventing it
 - split API changes into separate patches
 - simplify tagged iteration
 - use the proper xa_mark_t type for marks to make sparse happy

Diffstat:
 libxfs/xfs_ag.c |   94 +++++---------------------------------------------------
 libxfs/xfs_ag.h |   14 --------
 xfs_icache.c    |   85 +++++++++++++++++++++++++++++++++++---------------
 xfs_mount.h     |    3 -
 xfs_super.c     |    3 -
 xfs_trace.h     |    4 +-
 6 files changed, 72 insertions(+), 131 deletions(-)