xfs: collapse allocsize and biosize mount option handling

The allocsize and biosize mount options are handled identically,
other than allocsize accepting suffixes.  suffix_kstrtoint handles
bare numbers just fine too, so these can be collapsed.

Signed-off-by: Eric Sandeen <sandeen@redhat.com>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Dave Chinner <david@fromorbit.com>