fbdev: add FBIOCOPYAREA ioctl

Based on the patch authored by Ali Gholami Rudi at
    https://lkml.org/lkml/2009/7/13/153



Provide an ioctl for userspace applications, but only if this operation
is hardware accelerated (otherwide it does not make any sense).

Signed-off-by: Siarhei Siamashka <siarhei.siamashka@gmail.com>

bcm2708_fb: Add ioctl for reading gpu memory through dma