tridentfb: improved register values on TGUI 9680

Improved values for some registers after Xorg Trident driver.  The main
problem was that values set by BIOS have been ignored.

This patch completely remove random pixels ("snow") on the TGUI 9680 and
9440 (not supported yet by the driver).  It does not help with the "snow"
on 3DImage and Blade3D cards.

There is also small improvement in timing calculations (hblank start and
vblank start)

Signed-off-by: Krzysztof Helt <krzysztof.h1@wp.pl>
Cc: "Antonino A. Daplas" <adaplas@pol.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>