dmaengine: apple-admac: Handle 'global' interrupt flags

In addition to TX channel and RX channel interrupt flags there's
another class of 'global' interrupt flags with unknown semantics. Those
weren't being handled up to now, and they are the suspected cause of
stuck IRQ states that have been sporadically occurring. Check the global
flags and clear them if raised.

Fixes: b127315d

 ("dmaengine: apple-admac: Add Apple ADMAC driver")
Signed-off-by: Martin Povišer <povik+lin@cutebit.org>
Link: https://lore.kernel.org/r/20230224152222.26732-1-povik+lin@cutebit.org
Signed-off-by: Vinod Koul <vkoul@kernel.org>