viafb: unify modesetting functions

viafb: unify modesetting functions

This patch unifies some cleaned up modesetting functions to prepare for
moving them to an extra file. This includes make them use via_io and
changing there names to reflect that they do not depend on anything
framebuffer specific.

Signed-off-by: Florian Tobias Schandinat <FlorianSchandinat@gmx.de>