KVM: x86/mmu: Set CR4.PKE/LA57 in MMU role iff long mode is active

Don't set cr4_pke or cr4_la57 in the MMU role if long mode isn't active,
which is required for protection keys and 5-level paging to be fully
enabled.  Ignoring the bit avoids unnecessary reconfiguration on reuse,
and also means consumers of mmu_role don't need to manually check for
long mode.

Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20210622175739.3610207-28-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>