drm/i915: Set INSTPM_FORCE_ORDERING via LRI on gen8, drop it on gen9+

INSTPM is saved in the logical context so we should initialize it using
LRIs on gen8. It actually defaults to 1 starting from HSW, but let's
keep the write around anyway.

Also drop the INSTPM_FORCE_ORDERING setup entirely on gen9+ since it's
now a reserved bit.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Damien Lespiau <damien.lespiau@intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>