ARM: ux500: Pass DMA memcpy channels though Device Tree

It's now possible to configure memcpy channels dynamically with DT.
We're providing them despite the fact that they're the same as the
hard-coded channels, as they will be removed once the u8500 platform
goes DT-only.

Signed-off-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>