dmaengine: apple-admac: Avoid accessing registers in probe

dmaengine: apple-admac: Avoid accessing registers in probe

commit 8d55e8a16f019211163f1180fd9f9fbe05901900 upstream.

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>