dmaengine: PL08x: ignore 'direction' argument in dma_slave_config

Ignore the direction argument in dma_slave_config, and configure both
directions independently.  We still check that the configuration for
the intended direction is valid; this check will eventually be dropped.
This check is just for debugging at present.

Acked-by: Linus Walleij <linus.walleij@linaro.org>
Tested-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>