KVM: SVM: Invert handling of SEV and SEV_ES feature flags

Leave SEV and SEV_ES '0' in kvm_cpu_caps by default, and instead set them
in sev_set_cpu_caps() if SEV and SEV-ES support are fully enabled.  Aside
from the fact that sev_set_cpu_caps() is wildly misleading when it *clears*
capabilities, this will allow compiling out sev.c without falsely
advertising SEV/SEV-ES support in KVM_GET_SUPPORTED_CPUID.

Signed-off-by: Sean Christopherson <seanjc@google.com>
Reviewed-by: Michael Roth <michael.roth@amd.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Message-ID: <20240404121327.3107131-2-pbonzini@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>