dmaengine: omap-dma: move IRQ handling to omap-dma

Move the interrupt handling for OMAP2+ into omap-dma, rather than using
the legacy support in the platform code.

Acked-by: Tony Lindgren <tony@atomide.com>
Acked-by: Vinod Koul <vinod.koul@intel.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>