dt-bindings: interrupt-controller: add binding for mt6765

Update the dt-binding documentation of sysirq for mt6765

Signed-off-by: Mars Cheng <mars.cheng@mediatek.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>