dmaengine: axi-dmac: Request IRQ with IRQF_SHARED

Request IRQ with IRQF_SHARED flag to enable setups with multiple
instances of the core sharing a single IRQ line.
This works out since the IRQ handler already checks if there is
an actual IRQ pending and returns IRQ_NONE otherwise.

Acked-by: Lars-Peter Clausen <lars@metafoo.de>
Signed-off-by: Moritz Fischer <mdf@kernel.org>
Signed-off-by: Vinod Koul <vkoul@kernel.org>