drm/i915/gvt: always pass struct intel_display * to register macros

drm/i915/gvt: always pass struct intel_display * to register macros

The long term goal is to remove the __to_intel_display() generics from
display macros, such as register macros. This requires that all such
macro usage passes struct intel_display * rather than struct
drm_i915_private * to the macros.

The short term goal is to hide the struct drm_i915_private access in
intel_display_conversions.h into a function. This is problematic with
gvt, because it's a separate module, and the conversion function would
need to be exported.

Make the conversion to always passing struct intel_display * in gvt to
unblock both of the above.

Reviewed-by: Luca Coelho <luciano.coelho@intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/266616e14db8d9a342fd93ec9752f561149a799b.1732104170.git.jani.nikula@intel.com