improve log context annotations

Hi Carlos,

this series improves the lock annotations in the XFS code.

Note that right now this is all mostly unused - the less stringent sparse
lock context checks got disabled when the clang version was merged, and
we're not quite ready to enable the latter yet due to our conditional
locking in the ilock helper and the locking contexts transferred to the
transaction for the inode and dquot locks, but I'm working on that.

In the meantime having these corrected at least serves as useful
documentation.

Diffstat:
 xfs_extent_busy.c |    4 ++--
 xfs_icache.c      |    3 ++-
 xfs_log.c         |   33 +++++++++++++++++++++------------
 xfs_log_cil.c     |    3 ++-
 xfs_log_priv.h    |    4 ++--
 xfs_mru_cache.c   |    2 +-
 xfs_trans_ail.c   |    4 +++-
 xfs_zone_alloc.c  |    2 ++
 8 files changed, 35 insertions(+), 20 deletions(-)