KVM: x86: Expose CLDEMOTE CPU feature to guest VM

The CLDEMOTE instruction hints to hardware that the cache line that
contains the linear address should be moved("demoted") from
the cache(s) closest to the processor core to a level more distant
from the processor core. This may accelerate subsequent accesses
to the line by other cores in the same coherence domain,
especially if the line was written by the core that demotes the line.

This patch exposes the cldemote feature to the guest.

The release document ref below link:
https://software.intel.com/sites/default/files/managed/c5/15/\
architecture-instruction-set-extensions-programming-reference.pdf
This patch has a dependency on https://lkml.org/lkml/2018/4/23/928



Signed-off-by: Jingqi Liu <jingqi.liu@intel.com>
Reviewed-by: Wei Wang <wei.w.wang@intel.com>
Signed-off-by: Radim Krčmář <rkrcmar@redhat.com>