dmaengine: apple-admac: Avoid accessing registers in probe

dmaengine: apple-admac: Avoid accessing registers in probe

The ADMAC attached to the AOP has complex power sequencing, and is
power gated when the probe callback runs. Move the register reads
to other functions, where we can guarantee that the hardware is
switched on.

Fixes: 568aa6dd641f ("dmaengine: apple-admac: Allocate cache SRAM to channels")
Signed-off-by: Sasha Finkelstein <fnkl.kernel@gmail.com>
Link: https://lore.kernel.org/r/20241124-admac-power-v1-1-58f2165a4d55@gmail.com
Signed-off-by: Vinod Koul <vkoul@kernel.org>