KVM: x86: Add supported_vm_types to kvm_caps

This simplifies the implementation of KVM_CHECK_EXTENSION(KVM_CAP_VM_TYPES),
and also allows the vendor module to specify which VM types are supported.

Suggested-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Message-ID: <20240404121327.3107131-9-pbonzini@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>