drm/i915/gvt: add 0xe4f0 into gen9 render list

Guest may set this register on KBL platform, it can impact hardware
behavior, so add it into the gen9 render list. Otherwise gpu hang issue may
happen during different vgpu switch.

v2: separate it from patch set.

Cc: Zhi Wang <zhi.a.wang@intel.com>
Cc: Zhenyu Wang <zhenyuw@linux.intel.com>
Signed-off-by: Weinan Li <weinan.z.li@intel.com>
Signed-off-by: Zhenyu Wang <zhenyuw@linux.intel.com>