dmaengine: qcom_bam_dma: Add descriptor flag APIs

This patch adds APIs that allow for BAM hardware flags to be set per
descriptor.  Each one of the new flags informs the attached peripheral of a
special behavior that is required.

The EOT flag requests that the peripheral assert an end of transaction interrupt
when that descriptor is complete.  It also results in special signaling protocol
that is used between the attached peripheral and the core using the DMA
controller.

The NWD flag requests that the peripheral wait until the data has been fully
processed before signaling an interrupt.

The CMD flag informs the peripheral that the descriptor payload contains
command descriptors and not data descriptors.

Signed-off-by: Andy Gross <agross@codeaurora.org>