drm/i915/display: convert assert_transcoder*() to struct intel_display

drm/i915/display: convert assert_transcoder*() to struct intel_display

Going forward, struct intel_display is the main display device data
pointer. Convert the assert_transcoder*() helpers to struct
intel_display, allowing further conversions elsewhere.

Do a few small opportunistic conversions right away.

Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/430c2f3c899bc98beeb6ba8608f841c9271d0971.1739378095.git.jani.nikula@intel.com