KVM: x86 emulator: implement MMX MOVQ (opcodes 0f 6f, 0f 7f)

Needed by some framebuffer drivers.  See

https://bugzilla.kernel.org/show_bug.cgi?id=42779



Signed-off-by: Avi Kivity <avi@redhat.com>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>