KVM: VMX: Invert handling of CR0.WP for EPT without unrestricted guest

Opt-in to forcing CR0.WP=1 for shadow paging, and stop lying about WP
being "always on" for unrestricted guest.  In addition to making KVM a
wee bit more honest, this paves the way for additional cleanup.

No functional change intended.

Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20210713163324.627647-22-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>