Use fletcher_4 routines natively with `abd_iterate_func()`

Use fletcher_4 routines natively with `abd_iterate_func()`

This patch adds the necessary infrastructure for ABD to make use
of the vectorized fletcher 4 routines.

- export ABD compatible interface from fletcher_4
- add ABD fletcher_4 tests for data and metadata ABD types.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Original-patch-by: Gvozden Neskovic <neskovic@gmail.com>
Signed-off-by: David Quigley <david.quigley@intel.com>
Closes #5589