dmaengine: PL08x: get src/dst addr direct from dma_slave_config struct

Add a dma_slave_config struct to struct pl08x_dma_chan, and move the
src_addr/dst_addr arguments into this struct.  This is a step away
from using the dma_slave_config's direction member.

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>