drm/i915: Add GVT resume routine to i915

This patch add gvt resume wrapper into i915_drm_resume().
GVT relies on i915 so resume gvt at last.

V2:
- Direct call into gvt suspend/resume wrapper in intel_gvt.h/intel_gvt.c.
The wrapper and implementation will check and call gvt routine. (zhenyu)

V3:
Refresh.

V4:
Rebase.

V5:
Fail intel_gvt_suspend() if fail to save GGTT.

V6:
Save host entry to per-vGPU gtt.ggtt_mm on each host_entry update so
only need the resume routine.

V7:
Refresh.

Reviewed-by: Zhenyu Wang <zhenyuw@linux.intel.com>
Signed-off-by: Hang Yuan <hang.yuan@linux.intel.com>
Signed-off-by: Colin Xu <colin.xu@intel.com>
Signed-off-by: Zhenyu Wang <zhenyuw@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20201027045406.159566-1-colin.xu@intel.com