lib/Kconfig.debug: document panic= command line option and procfs entry for PANIC_TIMEOUT

lib/Kconfig.debug: document panic= command line option and procfs entry for PANIC_TIMEOUT

PANIC_TIMEOUT can also be controlled with the panic= kernel command line
option and the file /proc/sys/kernel/panic.  Let's document both of these
in the Kconfig help text.

Link: https://lkml.kernel.org/r/20240607152443.925168-1-bmasney@redhat.com
Signed-off-by: Brian Masney <bmasney@redhat.com>
Reviewed-by: Javier Martinez Canillas <javierm@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>