viafb: rework output device routing

This patch rips the device routing out of the 3 main functions to
separate functions to make them available for transition to a better
controlling scheme.

Signed-off-by: Florian Tobias Schandinat <FlorianSchandinat@gmx.de>
Cc: Joseph Chan <JosephChan@via.com.tw>
1 file changed