drm/i915/wm: convert i9xx_wm.h external interfaces to struct intel_display

drm/i915/wm: convert i9xx_wm.h external interfaces to struct intel_display

Going forward, struct intel_display is the main display device data
pointer. Convert the i9xx_wm.h interface to struct intel_display.

With this, we can make intel_wm.c independent of i915_drv.h.

v2: Also remove i915_drv.h, fix commit message

Reviewed-by: Suraj Kandpal <suraj.kandpal@intel.com>
Link: https://lore.kernel.org/r/3e30634d85c0e0aac9c95f9a2f928131ba400271.1744119460.git.jani.nikula@intel.com
Signed-off-by: Jani Nikula <jani.nikula@intel.com>