KVM: VMX: Unconditionally clear CPUID.INVPCID if !CPUID.PCID

KVM: VMX: Unconditionally clear CPUID.INVPCID if !CPUID.PCID

If PCID is not exposed to the guest, clear INVPCID in the guest's CPUID
even if the VMCS INVPCID enable is not supported.  This will allow
consolidating the secondary execution control adjustment code without
having to special case INVPCID.

Technically, this fixes a bug where !CPUID.PCID && CPUID.INVCPID would
result in unexpected guest behavior (#UD instead of #GP/#PF), but KVM
doesn't support exposing INVPCID if it's not supported in the VMCS, i.e.
such a config is broken/bogus no matter what.

Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
Message-Id: <20200923165048.20486-3-sean.j.christopherson@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>