drm/i915/gvt: addressed guest GPU hang with HWS index mode

with the introduce of "switch to use HWS indices rather than address",
guest GPU hang observed when running workloads which will update the
seqno to the real HW HWSP, not vitural GPU HWSP and then cause GPU hang.

this patch is to revoke index mode in PIPE_CTRL and MI_FLUSH_DW and
patch guest GPU HWSP address value to these commands.

Fixes: 54939ea0 ("drm/i915: Switch to use HWS indices rather than addresses")
Reviewed-by: Zhenyu Wang <zhenyuw@linux.intel.com>
Signed-off-by: Xiaolin Zhang <xiaolin.zhang@intel.com>
Signed-off-by: Zhenyu Wang <zhenyuw@linux.intel.com>