ARM: shmobile: irqpin: add a DT property to enable masking on parent

To disable spurious interrupts, that get triggered on certain hardware, the
irqpin driver masks them on the parent interrupt controller. To specify
such broken devices a .control_parent parameter can be provided in the
platform data. In the DT case we need a property, to do the same.

Signed-off-by: Guennadi Liakhovetski <g.liakhovetski@gmx.de>
Acked-by: Magnus Damm <damm@opensource.se>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>