stifb: Implement hardware accelerated copyarea

This patch adds hardware assisted scrolling. The code is based upon the
following investigation: https://parisc.wiki.kernel.org/index.php/NGLE#Blitter



A simple 'time ls -la /usr/bin' test shows 1.6x speed increase over soft
copy and 2.3x increase over FBINFO_READS_FAST (prefer soft copy over
screen redraw) on Artist framebuffer.

Signed-off-by: Alex Ivanov <lausgans@gmail.com>
Signed-off-by: Helge Deller <deller@gmx.de>