dmaengine: PL08x: Rework LLI handling to be less fragile

Currently memory allocated for LLIs is casted to an array of structs,
which is fragile and also limits the driver to a single, predefined LLI
layout, while there are some variants of PL08x, which have more fields
in LLI (namely PL080S with its extra CCTL2).

This patch makes LLIs a sequence of 32-bit words, which is just filled
with appropriate values in appropriate order and padded with required
amount of dummy words (currently zero, but PL080S will make better use
of this).

Suggested-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Tomasz Figa <tomasz.figa@gmail.com>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>