drm/i915/dpt: convert intel_dpt.[ch] interfaces to struct intel_display

drm/i915/dpt: convert intel_dpt.[ch] interfaces to struct intel_display

Going forward, struct intel_display is the main display device data
pointer. Convert the intel_dpt.[ch] interfaces to struct intel_display,
though the file being very i915 specific, it's hard to convert the
implementation.

Reviewed-by: Suraj Kandpal <suraj.kandpal@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/df2bf715639caeb662f08b776ba81bfe3c9288b9.1740502116.git.jani.nikula@intel.com
Signed-off-by: Jani Nikula <jani.nikula@intel.com>