drm/i915/gvt: handle force-nonpriv registers, cmd parser part

this patch adds force non-priv registers check in LRI cmds handler

v4:
transform is_force_nonpriv_mmio() from macro to inline fuction to eliminate
checkpatch warning

v3:
per zhenyu's comment, fix some style warnings

v2:
per zhenyu's comment, refine the code to remove cascaded ifs

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