dmaengine: edma: Do not register second device when booted with DT

DT boot does not yet support more than one edma device. To avoid issues at
runtime we should not register the second device when the kernel is booted
with DT.

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