drm/i915/fbc: convert intel_fbc.[ch] to struct intel_display

drm/i915/fbc: convert intel_fbc.[ch] to struct intel_display

Going forward, struct intel_display is the main display device data
pointer. Convert as much as possible of intel_fbc.[ch] to struct
intel_display. In a few places, change the variable declaration order to
prefer having display first.

Reviewed-by: Suraj Kandpal <suraj.kandpal@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/4dfd7d62e99b75d26563bdf29f541ed2ffbe548e.1740502116.git.jani.nikula@intel.com
Signed-off-by: Jani Nikula <jani.nikula@intel.com>