Accelerate framebuffer copyarea function with DMA and add ioctl to access it from userspace

It is a faster windows dragging and scrolling enabler for the X server. More details and some discussion can be found in the forum: http://www.raspberrypi.org/phpBB3/viewtopic.php?p=371531#p371531

I believe that these patches are reasonably clean and ready for use. But would be glad to fix/update them as seen necessary, hence posting for early review.