dmaengine: ste_dma40: add software lli support

This patch add support to manage LLI by SW for select phy channels.

There is a HW issue in certain controllers due to which on certain
occassions HW LLI cannot be used on some physical channels.  To avoid
the HW issue on a specific phy channel, the phy channel number can be
added to the list of soft_lli_channels and there after all the transfers
on that channel will use software LLI, for peripheral to memory
transfers.

SoftLLI introduces relink overhead, that could impact performace for
certain use cases.

This is based on a previous patch of Narayanan Gopalakrishnan.

Cc: Shreshtha Kumar Sahu <shreshthakumar.sahu@stericsson.com>
Acked-by: Linus Walleij <linus.walleij@linaro.org>
Acked-by: Vinod Koul <vinod.koul@intel.com>
Signed-off-by: Fabio Baltieri <fabio.baltieri@linaro.org>