x86: restore -- Allow to restore fpu even if image is incomatible with cpu state

Sometime, especially when testing, we migrate checkpointed tasks between
nodes which have different CPU capabilities. In particular some CPUs have
xsave feature while others -- do not. So to be able to continue migration
procedure even in such conditions one should specify

	--cpu-cap ^fpu

on command line which would force criu to restore FPU state ignoring extended
status present in image file.

Signed-off-by: Cyrill Gorcunov <gorcunov@openvz.org>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>