KVM: x86: Introduce supported_quirks to block disabling quirks

Introduce supported_quirks in kvm_caps to store platform-specific force-enabled
quirks.

No functional changes intended.

Signed-off-by: Yan Zhao <yan.y.zhao@intel.com>
Message-ID: <20250224070832.31394-1-yan.y.zhao@intel.com>
[Remove unsupported quirks at KVM_ENABLE_CAP time. - Paolo]
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>