atyfb: speed up Mach64 cursor

Save one fifo entry on cursor enabling and disabling.

Save another fifo entry for FB_CUR_SETPOS operation by removing redundant one.

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>