tridentfb: add acceleration for TGUI families

This patch adds acceleration for TGUI 9440 and 96xx chips.  These chips
requires line length to be power of 2, so this is also changed.

It also moves the troubling enable_mmio() function to its final
destination.

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>