dmaengine: ti-dma-crossbar: dra7: Support for reserving DMA event ranges

In eDMA the events are directly mapped to a DMA channel (for example DMA
event 14 can only be handled by DMA channel 14). If the memcpy is enabled
on the eDMA, there is a possibility that the crossbar driver would assign
DMA event number already allocated in eDMA for memcpy. Furthermore the
eDMA can be shared with DSP in which case the crossbar driver should also
avoid mapping xbar events to DSP used event numbers (or channels).

Signed-off-by: Peter Ujfalusi <peter.ujfalusi@ti.com>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>