dt-bindings: interrupt-controller: Update csky mpintc

Add trigger type setting for csky,mpintc. The driver also could
support #interrupt-cells <1> and it wouldn't invalidate existing
DTs. Here we only show the complete format.

Signed-off-by: Guo Ren <ren_guo@c-sky.com>
Reviewed-by: Rob Herring <robh+dt@kernel.org>
Cc: Marc Zyngier <marc.zyngier@arm.com>