KVM selftests "tree"-wide changes for 6.14:
- Rework vcpu_get_reg() to return a value instead of using an out-param, and
update all affected arch code accordingly.
- Convert the max_guest_memory_test into a more generic mmu_stress_test.
The basic gist of the "conversion" is to have the test do mprotect() on
guest memory while vCPUs are accessing said memory, e.g. to verify KVM
and mmu_notifiers are working as intended.
- Play nice with treewrite builds of unsupported architectures, e.g. arm
(32-bit), as KVM selftests' Makefile doesn't do anything to ensure the
target architecture is actually one KVM selftests supports.
- Use the kernel's $(ARCH) definition instead of the target triple for arch
specific directories, e.g. arm64 instead of aarch64, mainly so as not to
be different from the rest of the kernel.