drm/i915/gvt: Fix check error on opregion.c

As we switched to memremap for opregion, shouldn't use any __iomem
for that, and move to use memcpy instead.

This fixed static check errors for:

  CHECK   drivers/gpu/drm/i915//gvt/opregion.c
  drivers/gpu/drm/i915//gvt/opregion.c:142:31: warning: incorrect type in argument 1 (different address spaces)
  drivers/gpu/drm/i915//gvt/opregion.c:142:31:    expected void *addr
  drivers/gpu/drm/i915//gvt/opregion.c:142:31:    got void [noderef] <asn:2>*opregion_va
  drivers/gpu/drm/i915//gvt/opregion.c:160:35: warning: incorrect type in assignment (different address spaces)
  drivers/gpu/drm/i915//gvt/opregion.c:160:35:    expected void [noderef] <asn:2>*opregion_va
  drivers/gpu/drm/i915//gvt/opregion.c:160:35:    got void *

Signed-off-by: Zhenyu Wang <zhenyuw@linux.intel.com>