staging: drm/imx: use generic irqchip

This depends on the patch "genirq: Generic chip: Add linear irq domain support"
and removes the custom IPU irq_chip and irq_domain_ops. Instead, the generic
irq chip implementation is reused.

Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>
Acked-by: Grant Likely <grant.likely@secretlab.ca>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>