viafb: fix acceleration for some chips

Fix a regression in hardware acceleration which made the accelerated
framebuffer unusable on some chips.  These need extra initialization and
an extra flag which is no longer needed/available on current chips.

Signed-off-by: Erik-Jan Post <ej.lfs@xs4all.nl>
Signed-off-by: Florian Tobias Schandinat <FlorianSchandinat@gmx.de>
Cc: Scott Fang <ScottFang@viatech.com.cn>
Cc: Joseph Chan <JosephChan@via.com.tw>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>