drm/i915: Do not enable movntdqa optimization in hypervisor guest

Our QA reported a problem caused by movntdqa instructions. Currently,
the KVM hypervisor doesn't support VEX-prefix instructions emulation.
If users passthrough a GPU to guest with vfio option 'x-no-mmap=on',
then all access to the BARs will be trapped and emulated. The KVM
hypervisor would raise an inertal error to qemu which cause the guest
killed. (Since 'movntdqa' ins is not supported.)

This patch try not to enable movntdqa optimization if the driver is
running in hypervisor guest.

Signed-off-by: Changbin Du <changbin.du@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/1513924309-3113-1-git-send-email-changbin.du@intel.com
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>