drm/i915/mtl: Update cache coherency setting for context structure

As context structure is shared memory for CPU/GPU, Wa_22016122933 is
needed for this memory block as well.

Signed-off-by: Zhanjun Dong <zhanjun.dong@intel.com>
CC: Fei Yang <fei.yang@intel.com>
Reviewed-by: Fei Yang <fei.yang@intel.com>
Signed-off-by: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230706174704.177929-1-zhanjun.dong@intel.com