KVM: x86 emulator: implement 'movnti mem, reg'

Implement emulation of instruction:
    movnti m32/m64, r32/r64
    opcode: 0x0f 0xc3

Signed-off-by: Sheng Yang <sheng.yang@intel.com>
Signed-off-by: Avi Kivity <avi@qumranet.com>