drm/i915: Remove DDI power domain exclusion SKL_DISPLAY_ALWAYS_ON_POWER_DOMAINS

All the DDI power domains are already excluded from
SKL_DISPLAY_ALWAYS_ON_POWER_DOMAINS on account of
excluding SKL_DISPLAY_POWERWELL_1_POWER_DOMAINS and
SKL_DISPLAY_POWERWELL_2_POWER_DOMAINS, no need to spell them out again.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Patrik Jakobsson <patrik.jakobsson@linux.intel.com>
Signed-off-by: Imre Deak <imre.deak@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1447084107-8521-6-git-send-email-patrik.jakobsson@linux.intel.com