exynos: fimg2d: add g2d_set_direction

This allows setting the two direction registers, which specify how
the engine blits pixels. This can be used for overlapping blits,
which happen e.g. when 'moving' a rectangular region inside a
fixed buffer.

Reviewed-by: Hyungwon Hwang <human.hwang@samsung.com>
Signed-off-by: Tobias Jakobi <tjakobi@math.uni-bielefeld.de>
Signed-off-by: Hyungwon Hwang <human.hwang@samsung.com>