SHA256 QAT acceleration

SHA256 QAT acceleration

This patch enables acceleration of SHA256 checksums using Intel
Quick Assist Technology. This patch also fixes up and refactors
some of the code from QAT encryption to make the behavior
consistent.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Chengfeix Zhu <chengfeix.zhu@intel.com>
Signed-off-by: Weigang Li <weigang.li@intel.com>
Signed-off-by: Tom Caputi <tcaputi@datto.com>
Closes #7295