WIP: extend GCM assembly implementation to not require MOVBE

[adamdmoss]

Follow-up to #9749 since I'd started this implementation anyway.
Right now this PR exists to get into autobuild/testing - not quite ready for review etc. Will expand the PR real soon now.

Motivation and Context

Description

How Has This Been Tested?

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.
• I have run the ZFS Test Suite with this change applied.
• All commit messages are properly formatted and contain Signed-off-by.

[codecov]

Codecov Report

Merging #10025 into master will increase coverage by <1%.
The diff coverage is 73%.

@@           Coverage Diff            @@
##           master   #10025    +/-   ##
========================================
+ Coverage      79%      79%   +<1%     
========================================
  Files         386      386            
  Lines      122431   122441    +10     
========================================
+ Hits        97053    97289   +236     
+ Misses      25378    25152   -226

Flag	Coverage Δ
#kernel	79% <73%> (ø)	⬆️
#user	67% <73%> (ø)	⬆️

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[AttilaFueloep]

I think a have a less intrusive prototype (at least on the C side of things) which I prepared a week ago and opened a PR for in #10029 just now. Could you please have a look and tell me what you think?

I'm currently quite swamped so I couldn't find time to test this prototype and open a proper PR for it. I opened it now mainly to avoid double work. I'm afraid I won't find time to work on this in the next two or three weeks. It would be great If you could find the time to test it.

Sorry for the inconvenience.

[adamdmoss]

I'll close this in favor of #10029 unless anyone particularly prefers this approach.