drm/i915/display: convert dp_to_i915() to a macro

Avoid looking into the guts of struct drm_i915_private in
headers. Again, converting an inline function to a macro is less than
ideal, but avoids having to pull in i915_drv.h just for the to_i915()
part.
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/ed6c43455d13c90ebfed442b196625af5e6ede88.1638366969.git.jani.nikula@intel.com

drivers/gpu/drm/i915/display/intel_display_types.h

@@ -1883,11 +1883,7 @@ dp_to_lspcon(struct intel_dp *intel_dp)
 	return &dp_to_dig_port(intel_dp)->lspcon;
 }
 
-static inline struct drm_i915_private *
-dp_to_i915(struct intel_dp *intel_dp)
-{
-	return to_i915(dp_to_dig_port(intel_dp)->base.base.dev);
-}
+#define dp_to_i915(__intel_dp) to_i915(dp_to_dig_port(__intel_dp)->base.base.dev)
 
 #define CAN_PSR(intel_dp) ((intel_dp)->psr.sink_support && \
 			   (intel_dp)->psr.source_support)