drm/i915: Add missing pixel formats for skl+ "sprites"

All SKL+ universal planes support the same set of formats (with the
exception of NV12 which we don't expose yet). Make the format lists
for primary and sprites the same.

And make the format list const while at it.

v2: Deal with the "planar" format list as well

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Stanislav Lisovskiy <stanislav.lisovskiy@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20181005125817.22576-7-ville.syrjala@linux.intel.com