drm/i915/gvt: Inlcude intel_gvt.h where needed

drm/i915/gvt: Inlcude intel_gvt.h where needed

drivers/gpu/drm/i915/gvt/gvt.c:264:6: error: no previous prototype for ‘intel_gvt_clean_device’ [-Werror=missing-prototypes]
drivers/gpu/drm/i915/gvt/gvt.c:301:5: error: no previous prototype for ‘intel_gvt_init_device’ [-Werror=missing-prototypes]

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Jani Nikula <jani.nikula@intel.com>
Reviewed-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200304002331.2126072-1-chris@chris-wilson.co.uk