kvm: x86: Suppress CR3_PCID_INVD bit only when PCIDs are enabled

If the PCIDE bit is not set in CR4, then the MSb of CR3 is a reserved
bit. If the guest tries to set it, that should cause a #GP fault. So
mask out the bit only when the PCIDE bit is set.

Signed-off-by: Junaid Shahid <junaids@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>