drm/i915: eDP can be present on DDI-E

Enable eDP on DDI-E.

Also let's remove duplicated definitions to avoid later confusion.

Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Reviewed-by: Xiong Zhang <xiong.y.zhang@intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>