drm/virtio: Add drm_panic support

Virtio gpu supports the drm_panic module, which displays a message to
the screen when a kernel panic occurs. It is supported where it has
vmapped shmem BO.

Signed-off-by: Jocelyn Falempe <jfalempe@redhat.com>
Signed-off-by: Ryosuke Yasuoka <ryasuoka@redhat.com>
Tested-by: Dmitry Osipenko <dmitry.osipenko@collabora.com>
Reviewed-by: Dmitry Osipenko <dmitry.osipenko@collabora.com>
Signed-off-by: Dmitry Osipenko <dmitry.osipenko@collabora.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20250206104300.416014-1-ryasuoka@redhat.com