firewire, ieee1394: update Kconfig help

Update the Kconfig help texts of both stacks to encourage a general move
from the older to the newer drivers.  However, do not label ieee1394 as
"Obsolete" yet, as the newer drivers have not been deployed as default
stack in the majority of Linux distributions yet, and those who start
doing so now may still want to install the old drivers as fallback for
unforeseen issues.

Since Linux 2.6.32, FireWire audio devices can be driven by the newer
firewire driver stack too, hence remove an outdated comment about audio
devices.  Also remove comments about library versions since the 2nd
generation of libraw1394 and libdc1394 is now in common use; details on
library versions can be read at the wiki link from the help texts.

Signed-off-by: Stefan Richter <stefanr@s5r6.in-berlin.de>