sk98lin: mark deprecated in Kconfig

sk98lin is scheduled for removal in July 2007. This patch makes the
deprecation more obvious in the configuration interface. FWIW, Gentoo have
been shipping a patch very similar to this for a long time.

Signed-off-by: Daniel Drake <dsd@gentoo.org>
Signed-off-by: Jeff Garzik <jeff@garzik.org>