[Intel-gfx] Accelerated read from WC mem (i915_memcpy_from_wc()) may not work in virtualization world

[Du, Changbin]

Hi Chris,
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.)

One possible solution is that disable this optimization at i915_memcpy_init_early.
This require us to identify the CPUID to check if it is running in guest mode.

What do you think? Thanks.

-- 
Thanks,
Changbin Du