drm/i915/gvt: Cleanup unwanted public symbols

drivers/gpu/drm/i915/gvt/execlist.c:531:6: warning: symbol 'clean_execlist' was not declared. Should it be static?
drivers/gpu/drm/i915/gvt/execlist.c:545:6: warning: symbol 'reset_execlist' was not declared. Should it be static?
drivers/gpu/drm/i915/gvt/execlist.c:556:5: warning: symbol 'init_execlist' was not declared. Should it be static?
drivers/gpu/drm/i915/gvt/scheduler.c:248:6: warning: symbol 'release_shadow_wa_ctx' was not declared. Should it be static?

References: 06bb372f

 ("drm/i915/gvt: Introduce intel_vgpu_reset_submission")
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Zhi Wang <zhi.a.wang@intel.com>
Cc: Zhenyu Wang <zhenyuw@linux.intel.com>
Cc: intel-gvt-dev@lists.freedesktop.org
Signed-off-by: Zhenyu Wang <zhenyuw@linux.intel.com>