dmaengine: bam-dma: fix a warning about missing capabilities

Avoid the warning below triggered during dmaengine async device
registration.

WARNING: CPU: 1 PID: 1 at linux/drivers/dma/dmaengine.c:863
dma_async_device_register+0x2a8/0x4b8()
this driver doesn't support generic slave capabilities reporting

To do that fill mandatory .directions bit mask,
.src/dst_addr_widths and .residue_granularity dma_device fields
with appropriate values.

Signed-off-by: Stanimir Varbanov <stanimir.varbanov@linaro.org>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>