drm/i915/gen8: Add gen8_init_workarounds for common WA

WA in this function should be ordered based on register address.
The following order is suggested (Ville),

instpm
mi_mode
row chicken
half slice chicken
common slice chicken
hdc chicken
cache_mode_0
cache_mode_1
gt_mode

Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Arun Siluvery <arun.siluvery@linux.intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>