dmaengine: PL08x: Add cyclic transfer support

Many audio interface drivers require support of cyclic transfers to work
correctly, for example Samsung ASoC DMA driver. This patch adds support
for cyclic transfers to the amba-pl08x driver.

Signed-off-by: Alban Bedel <alban.bedel@avionic-design.de>
[tfiga: Rebase and slightly beautify the original patch.]
Signed-off-by: Tomasz Figa <tomasz.figa@gmail.com>
Acked-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>