drm/i915/display: convert intel_display.c to struct intel_display

drm/i915/display: convert intel_display.c to struct intel_display

Going forward, struct intel_display is the main display device data
pointer. Convert as much as possible of intel_display.c to struct
intel_display.

This exposes a couple of outside issues that need to be fixed as well,
in a register macro and a DSI PLL stub.

Reviewed-by: Nemesa Garg <nemesa.garg@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/1c0bafcb978d1cf4f4d54be2f497386f5302f7c8.1741084010.git.jani.nikula@intel.com
Signed-off-by: Jani Nikula <jani.nikula@intel.com>