drivers: dma: intel_adsp_gpdma: fix issue with stop and PM refcounts

The DMA interface allows start and stop to be called multiple
times and driver should ensure nothing bad happens if the calls
are not balanced.

Fix an issue where after a start-stop sequence the DMA would be
powered down, and then a subsequent stop would result in a crash
as driver accesses registers of a powered down hardware block.

Fix the issue by handling stop without actually reading the hw
registers to check channel status.

Link: https://github.com/thesofproject/sof/issues/8503


Signed-off-by: Kai Vehmanen <kai.vehmanen@linux.intel.com>