xfs: add rmap btree insert and delete helpers

Add a couple of helper functions to encapsulate rmap btree insert and
delete operations.  Add tracepoints to the update function.

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Brian Foster <bfoster@redhat.com>
Signed-off-by: Dave Chinner <david@fromorbit.com>