drm/i915: distinguish G33 and Pineview from each other

Pineview deserves to use its own platform enum (which was already added,
unused, previously). IS_G33() no longer matches Pineview, and gets
replaced by IS_G33() || IS_PINEVIEW() or equivalent. Pineview is no
longer an outlier among platform definitions.

Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1481143689-19672-1-git-send-email-jani.nikula@intel.com