dma: ti: k3-udma: Move DMA channel[0] allocation to probe and add udma_remove()

dma: ti: k3-udma: Move DMA channel[0] allocation to probe and add udma_remove()

Currently, the allocation of DMA channel[0] for memcpy is happening
in udma_transfer() for every transfer, which leads to a huge overhead
for each transfer, especially in case of nand page reads. So, move this
allocation to udma_probe(), as a result, the allocation is done once
during probe.

Introduce udma_remove() for the cleanup of allocated channel during
probe.

Signed-off-by: Santhosh Kumar K <s-k6@ti.com>
Signed-off-by: Prasanth Babu Mantena <p-mantena@ti.com>