xfs: combine grant heads into a single 64 bit integer

Prepare for switching the grant heads to atomic variables by
combining the two 32 bit values that make up the grant head into a
single 64 bit variable.  Provide wrapper functions to combine and
split the grant heads appropriately for calculations and use them as
necessary.

Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>

diff --cc fs/xfs/linux-2.6/xfs_trace.h
Simple merge

diff --cc fs/xfs/xfs_log.c
Simple merge

diff --cc fs/xfs/xfs_log_priv.h
Simple merge

diff --cc fs/xfs/xfs_log_recover.c
Simple merge