drm/i915: Organize GLK_COLORS.

Let's organize this in a way that it gets more obvious
when looking to the platform colors and in a easier
way to get inherited.

v2: Add comma at the end (Jani), when possible.

Cc: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: https://patchwork.freedesktop.org/patch/msgid/20171003063652.17248-3-rodrigo.vivi@intel.com