xfs: disambiguate units for ftrace fields tagged "offset"

Some of our tracepoints describe fields as "offset".  That name doesn't
describe any units, which makes the fields not very useful.  Rename the
fields to capture units and ensure the format is hexadecimal.

"fileoff" means file offset, in units of fs blocks
"pos" means file offset, in bytes
"forkoff" means inode fork offset, in bytes

The one remaining "offset" value is for iclogs, since that's the byte
offset of the end of where we've written into the current iclog.

Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Carlos Maiolino <cmaiolino@redhat.com>