Code improvement and bug fixes for QAT support

[cfzhu]

Motivation and Context

The current implementation initializes the QAT support for ZFS when the ZFS kernel module is loaded.
A prerequisite for this initialization to succeed is that the Intel QAT driver has already been initialized.
If this is not the case the QAT support for ZFS will not be available even if the QAT driver becomes available at a later stage. #8323

Description

Code improvement and bug fixes for QAT support

1. Support QAT when ZFS is root file-system:
   When ZFS module is loaded before QAT started, the QAT can
   be started again in post-process, e.g.:
   echo 0 > /sys/module/zfs/parameters/zfs_qat_compress_disable
   echo 0 > /sys/module/zfs/parameters/zfs_qat_encrypt_disable
   echo 0 > /sys/module/zfs/parameters/zfs_qat_checksum_disable
2. Verify alder checksum of the de-compress result
3. Allocate Digest, IV and AAD buffer in physical contiguous
   memory by QAT_PHYS_CONTIG_ALLOC.
4. Support session re-use feature in the new QAT driver, by
   waiting session lock before remove session.

How Has This Been Tested?

Ran local tests when the QAT driver is available at a later time, it can enable QAT
support by command 'echo 0 > /sys/module/zfs/parameters/zfs_qat_*_disable' when the
QAT started.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Performance enhancement (non-breaking change which improves efficiency)
• Code cleanup (non-breaking change which makes code smaller or more readable)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation (a change to man pages or other documentation)

Checklist:

• My code follows the ZFS on Linux code style requirements.
• I have updated the documentation accordingly.
• I have read the contributing document.
• I have added tests to cover my changes.
• All new and existing tests passed.
• All commit messages are properly formatted and contain Signed-off-by.