KVM: SVM: Check for SVM support in CPU compatibility checks

Check that SVM is supported and enabled in the processor compatibility
checks.  SVM already checks for support during hardware enabling,
i.e. this doesn't really add new functionality.  The net effect is that
KVM will refuse to load if a CPU doesn't have SVM fully enabled, as
opposed to failing KVM_CREATE_VM.

Opportunistically move svm_check_processor_compat() up in svm.c so that
it can be invoked during hardware enabling in a future patch.

Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20221130230934.1014142-39-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>