drm/i915/tgl: Fixing up list of PG3 power domains.

The DDI-IO power wells (PWR_WELL_CTL_DDI) are backing
the IO/PHY functionality, which doesn't need the PG3
power power well. Accordingly fixing up the list of
PG3 power domains.

Cc: Imre Deak <imre.deak@intel.com>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Anshuman Gupta <anshuman.gupta@intel.com>
Signed-off-by: Imre Deak <imre.deak@intel.com>
Reviewed-by: Imre Deak <imre.deak@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190811100232.27964-1-anshuman.gupta@intel.com