tridentfb: acceleration bug fixes

This patch fixes two problems when acceleration is enabled:

 - bit for bitblt direction is corrected
   so scrolling down works as expected on 3DImage chips

 - initialization of acceleration is done later
   this helps with initial console malfuntion (on Blade3D
   chips) well documented here:
   http://marc.info/?l=linux-fbdev-users&m=111386953124478&w=2

Signed-off-by: Krzysztof Helt <krzysztof.h1@wp.pl>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>