pm3fb: improvements and cleanups

This patch contains improvements:
- it adds ROP_XOR in pm3fb_fillrect()
- it conforms closer to coding style
- it removes redundant parentheses and setting bits with 0 value
- it checks if hardware acceleration is disabled in pm3fb_imageblit
- it adds module description

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>