drm/nouveau: use drm_dev_unplug() during device removal

mainline inclusion
from mainline
commit aff2299e
bugzilla: 185776 https://gitee.com/openeuler/kernel/issues/I4DDEL
CVE: CVE-2020-27820

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=aff2299e0d81b26304ccc6a1ec0170e437f38efc



--------------------------------

Nouveau does not currently support hot-unplugging, but it still makes
sense to switch from drm_dev_unregister() to drm_dev_unplug().
drm_dev_unplug() calls drm_dev_unregister() after marking the device as
unplugged, but only after any device critical sections are finished.

Since nouveau isn't using drm_dev_enter() and drm_dev_exit(), there are
no critical sections so this is nearly functionally equivalent. However,
the DRM layer does check to see if the device is unplugged, and if it is
returns appropriate error codes.

In the future nouveau can add critical sections in order to truly
support hot-unplugging.

Cc: stable@vger.kernel.org # 5.4+
Signed-off-by: Jeremy Cline <jcline@redhat.com>
Reviewed-by: Lyude Paul <lyude@redhat.com>
Reviewed-by: Ben Skeggs <bskeggs@redhat.com>
Tested-by: Karol Herbst <kherbst@redhat.com>
Signed-off-by: Karol Herbst <kherbst@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20201125202648.5220-2-jcline@redhat.com
Link: https://gitlab.freedesktop.org/drm/nouveau/-/merge_requests/14


Signed-off-by: Chen Jun <chenjun102@huawei.com>
Reviewed-by: weiyang wang <wangweiyang2@huawei.com>
Reviewed-by: Jason Yan <yanaijie@huawei.com>

Signed-off-by: Chen Jun <chenjun102@huawei.com>
Signed-off-by: Zheng Zengkai <zhengzengkai@huawei.com>