KVM: selftests: Add test for user space MSR handling

Now that we have the ability to handle MSRs from user space and also to
select which ones we do want to prevent in-kernel KVM code from handling,
let's add a selftest to show case and verify the API.

Signed-off-by: Alexander Graf <graf@amazon.com>

Message-Id: <20200925143422.21718-9-graf@amazon.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>