KVM: SEV: Turn sev_es_validate_vmgexit() into a dedicated predicate

KVM: SEV: Turn sev_es_validate_vmgexit() into a dedicated predicate

Now that sev_es_validate_vmgexit() is only responsible for checking that
all required GHCB fields are marked valid, turn it into a predicate whose
name reflects exactly that.

No functional change intended.

Reviewed-by: Tom Lendacky <thomas.lendacky@amd.com>
Reviewed-by: Michael Roth <michael.roth@amd.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-ID: <20260501202250.2115252-24-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Message-ID: <20260529183549.1104619-24-pbonzini@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>