spi_qsd: Add support for multiple BAM descriptors

Currently SPI driver is queuing a single BAM descriptor
at a time. The BAM engine supports queuing of multiple
transfer descriptors.

Add support to spi driver to queue multiple descriptors.

CRs-Fixed: 546346
Change-Id: Iaee9b3b362832262b75e46e19ad18552d037620b
Signed-off-by: Alok Chauhan <alokc@codeaurora.org>