KVM: x86 emulator: Add vmmcall/vmcall to x86_emulate (v3)

Add vmmcall/vmcall to x86_emulate.  Future patch will implement functionality
for these instructions.

Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
Signed-off-by: Avi Kivity <avi@qumranet.com>