drm/i915/display: convert global state to struct intel_display

Going forward, struct intel_display is the main display device
structure. Convert intel_global_state.[ch] to it.

This allows us to make intel_pmdemand.c completely independent of
i915_drv.h.

Cc: Gustavo Sousa <gustavo.sousa@intel.com>
Reviewed-by: Gustavo Sousa <gustavo.sousa@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/2b5e743b285a86a59ee87085727847c758c8d552.1735662324.git.jani.nikula@intel.com


Signed-off-by: Jani Nikula <jani.nikula@intel.com>