drm/i915: make intel_guc_reg.h self-contained

Add the minimal includes/declarations to make the header self-contained,
and ensure it stays that way.

v2: also include i915_reg.h (Michal)
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190626144020.2155-11-jani.nikula@intel.com

drivers/gpu/drm/i915/Makefile.header-test

@@ -21,6 +21,7 @@ header_test := \
 	intel_drv.h \
 	intel_guc_ct.h \
 	intel_guc_fwif.h \
+	intel_guc_reg.h \
 	intel_pm.h \
 	intel_runtime_pm.h \
 	intel_sideband.h \

drivers/gpu/drm/i915/intel_guc_reg.h

@@ -24,6 +24,11 @@
 #ifndef _INTEL_GUC_REG_H_
 #define _INTEL_GUC_REG_H_
 
+#include <linux/compiler.h>
+#include <linux/types.h>
+
+#include "i915_reg.h"
+
 /* Definitions of GuC H/W registers, bits, etc */
 
 #define GUC_STATUS			_MMIO(0xc000)