exynos/fimg2d: add g2d_move

We already have g2d_copy() which implements G2D copy
operations from one buffer to another. However we can't
do a overlapping copy operation in one buffer.

Add g2d_move() which acts like the standard memmove()
and properly handles overlapping copies.

Signed-off-by: Tobias Jakobi <tjakobi@math.uni-bielefeld.de>