This reverts commit defd28aa.

Recover the code to disable premapped mode.
Signed-off-by: Xuan Zhuo <xuanzhuo@linux.alibaba.com>
Acked-by: Michael S. Tsirkin <mst@redhat.com>
Tested-by: Takero Funaki <flintglass@gmail.com>
Link: https://patch.msgid.link/20240906123137.108741-2-xuanzhuo@linux.alibaba.comSigned-off-by: Jakub Kicinski <kuba@kernel.org>