dmaengine: ti-dma-crossbar: dra7: Use bitops instead of idr

commit ec9bfa1e1a796ef7acc2e55917c9b8be5a79e70eupstream.

The use of idr was nice, but it was a bit heavy and we did not need the
features it provides. Using simple bitmap to track allocated DMA channels
is adequate here and it will be easier to add support for reserving
channels later on.

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