ARCv2: IDU-intc: Add support for edge-triggered interrupts

This adds support for an optional extra interrupt cell to specify edge
vs level triggered. It is backward compatible with dts files with only
one cell, and will default to level-triggered in such a case.

Note that I had to make a change to idu_irq_set_affinity as well, as
this function was setting the interrupt type to "level" unconditionally,
since this was the only type supported previously.

Signed-off-by: Mischa Jonker <mischa.jonker@synopsys.com>
Reviewed-by: Vineet Gupta <vgupta@synopsys.com>
Signed-off-by: Vineet Gupta <vgupta@synopsys.com>