drm/i915/gvt: update F_CMD_WRITE_PATCH flag when parsing init ctx

if a vreg has write handler, set its flag F_CMD_WRITE_PATCH on when
parsing init ctx.

Cc: Kevin Tian <kevin.tian@intel.com>
Signed-off-by: Yan Zhao <yan.y.zhao@intel.com>
Signed-off-by: Zhenyu Wang <zhenyuw@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20201223034623.17368-1-yan.y.zhao@intel.com


Reviewed-by: Zhenyu Wang <zhenyuw@linux.intel.com>