- EAX=0Dh, ECX=1: output registers EBX/ECX/EDX are reserved.

- EAX=0Dh, ECX>1: output register ECX bit 0 is clear for all the CPUID
leaves we support, because variable "supported" comes from XCR0 and not
XSS.  Bits above 0 are reserved, so ECX is overall zero.  Output register
EDX is reserved.

Source: Intel Architecture Instruction Set Extensions Programming
Reference, ref. number 319433-022
Reviewed-by: Radim Krčmář <rkrcmar@redhat.com>
Tested-by: Wanpeng Li <wanpeng.li@linux.intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>