viafb: restore display on resume

This patch makes viafb restore the display on resume by calling
viafb_set_par. Resumeing has still its issues:
- will probably freeze most machines (for me on VX800 reliable on the
  second resume)
- under some configurations the screen appears on the wrong output
  device (reason unknown)

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