drm/i915/display: Separate xe and i915 common dpt code into own file

Here created intel_dpt_common.c to hold intel_dpt_configure which is
needed for both xe and i915.

Signed-off-by: Juha-Pekka Heikkila <juhapekka.heikkila@gmail.com>
Reviewed-by: Jouni Högander <jouni.hogander@intel.com>
Signed-off-by: Jouni Högander <jouni.hogander@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20231116150225.204233-1-juhapekka.heikkila@gmail.com