x86: Add tests for PKS

This unit-test is intended to test the KVM support for Protection Keys
for Supervisor Pages (PKS). If CR4.PKS is set in long mode, supervisor
pkeys are checked in addition to normal paging protections and Access or
Write can be disabled via a MSR update without TLB flushes when
permissions change.

Signed-off-by: Chenyi Qiang <chenyi.qiang@intel.com>
Message-Id: <20201105081805.5674-9-chenyi.qiang@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>