drm/i915/icl: DP_AUX_E is valid on ICL+

Add support for DP_AUX_E. Here we also introduce the bits for the AUX
power well E, however ICL power well support is still not enabled yet,
so the power well is not used.

Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
Cc: Dhinakaran Pandiyan <dhinakaran.pandiyan@intel.com>
Reviewed-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
Signed-off-by: James Ausmus <james.ausmus@intel.com>
Signed-off-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180612002512.29783-2-paulo.r.zanoni@intel.com