tdfxfb: 3 fixes

This patch fixes 3 issues:
- transparency handling in tdfxfb
- panning with more than 4096 virtual height and acceleration (acceleration
with x & y > 4096)
- exit paths on errors in tdfxfb_probe()

Additionally it sets a FBINFO_READS_FAST flag to use smart blitter scrolling
(speed up on tdfxfb).

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