mtd: nand: qcom: QPIC data descriptors handling

1. Add the data descriptor preparation function which will be used
   only by BAM DMA for forming the data SGL’s
2. Add clear BAM transaction and call it before every new request
3. Check DMA mode for ADM or BAM and call the appropriate
   descriptor formation function.

Reviewed-by: Archit Taneja <architt@codeaurora.org>
Signed-off-by: Abhishek Sahu <absahu@codeaurora.org>
Signed-off-by: Boris Brezillon <boris.brezillon@free-electrons.com>