drm/i915: make intel_guc_fwif.h self-contained

Add the minimal includes/declarations to make the header self-contained,
and ensure it stays that way.
Reviewed-by: NChris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: NJani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190626144020.2155-10-jani.nikula@intel.com

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

@@ -20,6 +20,7 @@ header_test := \
 	intel_csr.h \
 	intel_drv.h \
 	intel_guc_ct.h \
+	intel_guc_fwif.h \
 	intel_pm.h \
 	intel_runtime_pm.h \
 	intel_sideband.h \

drivers/gpu/drm/i915/intel_guc_fwif.h

@@ -23,6 +23,10 @@
 #ifndef _INTEL_GUC_FWIF_H
 #define _INTEL_GUC_FWIF_H
 
+#include <linux/bits.h>
+#include <linux/compiler.h>
+#include <linux/types.h>
+
 #define GUC_CLIENT_PRIORITY_KMD_HIGH	0
 #define GUC_CLIENT_PRIORITY_HIGH	1
 #define GUC_CLIENT_PRIORITY_KMD_NORMAL	2