dt-bindings: irqchip: convert st,stih407-irq-syscfg to DT schema

Convert deprecated format to DT schema format.

Signed-off-by: Raphael Gallais-Pou <rgallaispou@gmail.com>
Reviewed-by: Conor Dooley <conor.dooley@microchip.com>
Link: https://lore.kernel.org/r/20230905072740.23859-1-rgallaispou@gmail.com


Signed-off-by: Rob Herring <robh@kernel.org>