xfs: Add xfs_log_rlimit.c

xfs: Add xfs_log_rlimit.c

Add source files for xfs_log_rlimit.c The new file is used for log
size calculations and validation shared with userspace.

[dchinner: xfs_log_calc_max_attrsetm_res() does not modify the
tr_attrsetm reservation, just calculates the maximum. ]

[dchinner: rework loop in xfs_log_get_max_trans_res() ]

[dchinner: implement xfs_log_calc_unit_res() in util.c to give mkfs
a worse case calculation of the log size needed. ]

Signed-off-by: Jie Liu <jeff.liu@oracle.com>
Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Mark Tinguely <tinguely@sgi.com>
Signed-off-by: Rich Johnston <rjohnston@sgi.com>