drm/i915: Remove redundant forward declarations from display power headers

Remove the forward declarations for enums and structs from display power
header files that aren't used in prototypes.
Reviewed-by: Jouni Högander <jouni.hogander@intel.com>
Signed-off-by: Imre Deak <imre.deak@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230616185104.2502003-2-imre.deak@intel.com

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

@@ -12,9 +12,6 @@
 #include "intel_wakeref.h"
 
 enum aux_ch;
-enum dpio_channel;
-enum dpio_phy;
-enum i915_drm_suspend_mode;
 enum port;
 struct drm_i915_private;
 struct i915_power_well;

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

@@ -11,7 +11,6 @@
 #include "intel_dpio_phy.h"
 
 struct drm_i915_private;
-struct i915_power_well;
 struct i915_power_well_ops;
 struct intel_encoder;