KVM: x86/mmu: Use MMU's role to compute PKRU bitmask

Use the MMU's role to calculate the Protection Keys (Restrict Userspace)
bitmask instead of pulling bits from current vCPU state.  For some flows,
the vCPU state may not be correct (or relevant), e.g. EPT doesn't
interact with PKRU.  Case in point, the "ept" param simply disappears.

Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20210622175739.3610207-34-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>