drm/i915: Add missing forward declarations/includes to display power headers

Add the seq_file struct forward declaration to intel_display_power.h
fixing the build error below. While at it add the rest of missing
forward declarations/includes to the display power header files.

In file included from <command-line>:
./../drivers/gpu/drm/i915/display/intel_display_power.h:255:70: error: 'struct seq_file'
declared inside parameter list will not be visible outside of this definition or declaration [-Werror]
  255 | void intel_display_power_debug(struct drm_i915_private *i915, struct seq_file *m);
      |                                                                      ^~~~~~~~

Closes: https://lore.kernel.org/intel-gfx/89adc1ac-25a0-6eb6-4cc9-ab6cc8d49730@infradead.org/Reported-by: Randy Dunlap <rdunlap@infradead.org>
Acked-by: Randy Dunlap <rdunlap@infradead.org>
Tested-by: Randy Dunlap <rdunlap@infradead.org> # build-tested
Reviewed-by: Jouni Högander <jouni.hogander@intel.com>
Signed-off-by: Imre Deak <imre.deak@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230616185104.2502003-1-imre.deak@intel.com
(cherry picked from commit f4fab137)
Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>

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

@@ -6,6 +6,9 @@
 #ifndef __INTEL_DISPLAY_POWER_H__
 #define __INTEL_DISPLAY_POWER_H__
 
+#include <linux/mutex.h>
+#include <linux/workqueue.h>
+
 #include "intel_wakeref.h"
 
 enum aux_ch;
@@ -16,6 +19,7 @@ enum port;
 struct drm_i915_private;
 struct i915_power_well;
 struct intel_encoder;
+struct seq_file;
 
 /*
  * Keep the pipe, transcoder, port (DDI_LANES,DDI_IO,AUX) domain instances

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

@@ -12,6 +12,8 @@
 
 struct drm_i915_private;
 struct i915_power_well;
+struct i915_power_well_ops;
+struct intel_encoder;
 
 #define for_each_power_well(__dev_priv, __power_well)				\
 	for ((__power_well) = (__dev_priv)->display.power.domains.power_wells;	\