drm/i915/gvt: Add in context mmio 0x20D8 to gen9 mmio list

Depends on GEN family and I915_PARAM_HAS_CONTEXT_ISOLATION, Mesa driver
will decide whether constant buffer 0 address is relative or absolute,
and load GPU initial state by lri to context mmio INSTPM (GEN8)
or 0x20D8 (>=GEN9).
Mesa Commit fa8a764b62
("i965: Use absolute addressing for constant buffer 0 on Kernel 4.16+.")

INSTPM is already added to gen8_engine_mmio_list, but 0x20D8 is missed
in gen9_engine_mmio_list. From GVT point of view, different guest could
have different context so should switch those mmio accordingly.

v2: Update fixes commit ID.

Fixes: 17865713 ("drm/i915/gvt: vGPU context switch")
Reviewed-by: Zhenyu Wang <zhenyuw@linux.intel.com>
Signed-off-by: Colin Xu <colin.xu@intel.com>
Signed-off-by: Zhenyu Wang <zhenyuw@linux.intel.com>
(cherry picked from commit 1e8b15a1)

drivers/gpu/drm/i915/gvt/mmio_context.c

@@ -132,6 +132,7 @@ static struct engine_mmio gen9_engine_mmio_list[] __cacheline_aligned = {
 
 	{RCS0, GEN9_GAMT_ECO_REG_RW_IA, 0x0, false}, /* 0x4ab0 */
 	{RCS0, GEN9_CSFE_CHICKEN1_RCS, 0xffff, false}, /* 0x20d4 */
+	{RCS0, _MMIO(0x20D8), 0xffff, true}, /* 0x20d8 */
 
 	{RCS0, GEN8_GARBCNTL, 0x0, false}, /* 0xb004 */
 	{RCS0, GEN7_FF_THREAD_MODE, 0x0, false}, /* 0x20a0 */