Add opmask (k) registers to the register allocator

[anthonycanino]

This task will add the ability to specify opmask registers as LSRA constraints to the register allocator. This task has a dependency on #80821.

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Issue Details

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This task will add the ability to specify opmask registers as LSRA constraints to the register allocator. This task has a dependency on #80821.

Author:	anthonycanino
Assignees:	-
Labels:	area-CodeGen-coreclr, arch-avx512
Milestone:	8.0.0

[tannergooding]

This work has mostly been completed, what remains is allowing LSRA to use more than only K1

[BruceForstall]

@tannergooding Is this complete with #89059?

[tannergooding]

Yes it is. We're not allowing allocation of k0 at the moment, because its a bit special; but there's nothing blocking it from being used outside setting the right preferencing for when its invalid