drm/i915/gvt: force-nopriv register handling

drm/i915/gvt: force-nopriv register handling

add a whitelist to check the content of force-nonpriv registers

v3:
per He Min's comment, modify in_whitelist()'s return type to bool, and use
negative value as the return value for failure for force_nonpriv_write().

v2:
1. split a big patch into two smaller ones per zhenyu's comment.
this patch is the mmio handling part for force-nopriv registers

2. per zhenyu's comment, combine all non-priv registers into a single
MMIO_DFH entry

Signed-off-by: Zhao Yan <yan.y.zhao@intel.com>
Signed-off-by: Zhenyu Wang <zhenyuw@linux.intel.com>