ARM: ux500: Strip out duplicate USB DMA configuration

For the moment at least, the TX and RX channels for DB8500 USB are
identical, so this patch generalises them into a single structure
and passes it twice. Once as the TX and again for the RX configuration.
We're keeping the infrastructure the same i.e. passing the TX and RX
separately in case they start to differ on latter incarnations of the
platform.

Acked-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>