viafb: add a mapping of supported output devices

This patch maps supported output devices to IGP versions. This list may
contain errors as most of it is derived of the driver source but it should
be correct enough to provide a good help. The devices are exported via a
proc entry in the same format as those showing the output devices per IGA.

Signed-off-by: Florian Tobias Schandinat <FlorianSchandinat@gmx.de>
Acked-by: Jonathan Corbet <corbet@lwn.net>
Cc: Joseph Chan <JosephChan@via.com.tw>
Cc: Andrew Morton <akpm@linux-foundation.org>