Allow QAT to handle non page-aligned buffers

Allow QAT to handle non page-aligned buffers

This patch adds some handling to the QAT acceleration functions
that allows them to handle buffers that are not aligned with the
page cache. At the moment this never happens since callers only
happen to work with page-aligned buffers, but this code should
prevent headaches if this isn't always true in the future. This
patch also adds some cleanups to align the QAT compression code
with the encryption and checksumming code.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Weigang Li <weigang.li@intel.com>
Signed-off-by: Tom Caputi <tcaputi@datto.com>
Closes #7305