dmaengine: ste_dma40: Replace ST-E's home-brew DMA direction defs with generic ones

STEDMA40_*_TO_* direction definitions are identical in all but name to
the pre-defined generic DMA_*_TO_* ones. Let's make things easy by not
duplicating such things.

Cc: Dan Williams <djbw@fb.com>
Cc: Per Forlin <per.forlin@stericsson.com>
Cc: Rabin Vincent <rabin@rab.in>
Acked-by: Vinod Koul <vinod.koul@intel.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>