drm/i915/gvt: make interrupt.h self-contained

Add necessary #includes and forward declarations to make the header
compile on its own.
Reviewed-by: Zhenyu Wang <zhenyuw@linux.intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Zhenyu Wang <zhenyuw@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/3a1060d0e9b951d76815745f466efc17a7c85741.1607422863.git.jani.nikula@intel.com

drivers/gpu/drm/i915/Makefile

@@ -285,7 +285,6 @@ obj-$(CONFIG_DRM_I915_GVT_KVMGT) += gvt/kvmgt.o
 no-header-test := \
 	display/intel_vbt_defs.h \
 	gvt/gvt.h \
-	gvt/interrupt.h \
 	gvt/mmio_context.h \
 	gvt/mpt.h \
 	gvt/scheduler.h

drivers/gpu/drm/i915/gvt/interrupt.h

@@ -32,7 +32,10 @@
 #ifndef _GVT_INTERRUPT_H_
 #define _GVT_INTERRUPT_H_
 
-#include <linux/types.h>
+#include <linux/hrtimer.h>
+#include <linux/kernel.h>
+
+#include "i915_reg.h"
 
 enum intel_gvt_event_type {
 	RCS_MI_USER_INTERRUPT = 0,