KVM: selftests: Verify userspace can stuff IA32_FEATURE_CONTROL at will

Verify the KVM allows userspace to set all supported bits in the
IA32_FEATURE_CONTROL MSR irrespective of the current guest CPUID, and
that all unsupported bits are rejected.

Throw the testcase into vmx_msrs_test even though it's not technically a
VMX MSR; it's close enough, and the most frequently feature controlled by
the MSR is VMX.

Signed-off-by: Sean Christopherson <seanjc@google.com>
Link: https://lore.kernel.org/r/20220607232353.3375324-4-seanjc@google.com