drm/i915: make i915_vgpu.h self-contained

Add the minimal includes/declarations to make the header self-contained,
and ensure it stays that way.
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/20190626144020.2155-8-jani.nikula@intel.com

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

@@ -16,6 +16,7 @@ header_test := \
 	i915_reg.h \
 	i915_scheduler_types.h \
 	i915_utils.h \
+	i915_vgpu.h \
 	intel_csr.h \
 	intel_drv.h \
 	intel_pm.h \

drivers/gpu/drm/i915/i915_vgpu.h

@@ -24,6 +24,7 @@
 #ifndef _I915_VGPU_H_
 #define _I915_VGPU_H_
 
+#include "i915_drv.h"
 #include "i915_pvinfo.h"
 
 void i915_detect_vgpu(struct drm_i915_private *dev_priv);