dmaengine: axi-dmac: wrap entire dt parse in a function

dmaengine: axi-dmac: wrap entire dt parse in a function

All these attributes will be read from registers in newer core versions, so
just wrap the logic into a function.

Signed-off-by: Alexandru Ardelean <alexandru.ardelean@analog.com>
Link: https://lore.kernel.org/r/20200825151950.57605-5-alexandru.ardelean@analog.com
Signed-off-by: Vinod Koul <vkoul@kernel.org>