tridentfb: acceleration code improvements

This patch brings various acceleration improvements:
- set  copyarea/fillrect for non-accelerated framebuffer (fix)
- remove 15 bpp depth handling to simplify code as it hardly
  works (15 bpp handling was obviously missing in some switches)
- add fb_sync call and move waiting before accelerated function
  to make acceleration more asynchronous to cpu (few % of speed
  improvement)
- add cpu_relax() call in waiting loops
- make longer register names and name more registers
- move registers' definition to header
- general code improvements (shortening, simplifying)

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>