dmaengine: PL08x: convert to use vchan submitted/issued lists

Convert to use the virtual dma channel submitted/issued descriptor
lists rather than our own private lists, and use the virtual dma
channel support functions to manage these lists.

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>