drm/i915: Remove the XELPD specific AUX and DDI power domains

The spec calls the XELPD_D/E ports just D/E, the platform prefix in the
domain names was only needed by the port->domain mapping relying on
matching enum values for the whole port/domain range (and the
corresponding aliasing between the platform specific domain enums).
Since a previous patch we can define the port->domain mapping explicitly
so do this by reusing the already existing D/E power domain names.

Signed-off-by: Imre Deak <imre.deak@intel.com>
Reviewed-by: Jouni Högander <jouni.hogander@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220414210657.1785773-18-imre.deak@intel.com