dmaengine: ti: Add support for k3 event routers

In k3 architecture a DMA channel (in TR momde) can be triggered by global
events, origination from different modules.

The events for triggers can be sent from any module which is connected to
PSI-L fabric, but the event number to be sent is DMA channel specific, it
is only known after the channel itself is requested.

The router operation needs to be split up:
- route_allocate: configure the dma_spec for the DMA and store the
  configuration which is needed for the router's input
- set_event: callback used by the DMA driver to set the event number for
  the channel and enable the routing

Signed-off-by: Peter Ujfalusi <peter.ujfalusi@ti.com>
Link: https://lore.kernel.org/r/20201208090440.31792-16-peter.ujfalusi@ti.com
Signed-off-by: Vinod Koul <vkoul@kernel.org>