mshv-ioctls: Add support for aarch64

[jinankjain]

Summary of the PR

Remove conditional compilation for x86_64.

Requirements

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• [x] All commits in this PR have Signed-Off-By trailers (with git commit -s), and the commit message has max 60 characters for the summary and max 75 characters for each description line.
• [x] All added/changed functionality has a corresponding unit/integration test.
• [x] All added/changed public-facing functionality has entries in the "Upcoming Release" section of CHANGELOG.md (if no such section exists, please create one).
• [x] Any newly added unsafe code is properly documented.

[russell-islam]

@jinankjain This PR excludes some of the registers. After excluding the registers, rest of them are enough to boot arm64 guest? Don't we need additional registers somewhere?

[jinankjain]

I have just added a compilation support not functional support for ARM64. get and set_reg would have a different implementation for aarch64.