drm/panic: Add panic description

drm/panic: Add panic description

Now that kmsg dump callback has the description parameter, use it in
the user panic screen.
This is the string passed to panic(), like "VFS: Unable to mount root
fs on xxx" or "Attempted to kill init! exitcode=0xxxx".
It gives a hint on why the panic occurred, without being too cryptic.

Signed-off-by: Jocelyn Falempe <jfalempe@redhat.com>
Reviewed-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20240807134902.458669-6-jfalempe@redhat.com