dmaengine: shdma: fix a regression: initialise DMA channels for memcpy

A recent patch has introduced a regression, where repeating a memcpy DMA test with shdma module unloading between them skips the DMA channel configuration. Fix this regression by always configuring the channel during its allocation.

These definitions are needed to let the runtime PM subsystem turn off DMAC clocks, when it is suspended by the driver.