dt-bindings: gpio: pca95xx: add TI TCA6418

The TCA6418E is a 18-channel I2C I/O expander with integrated ESD
protection.

Signed-off-by: Maria Garcia <[e-mail]>
Acked-by: Conor Dooley <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Bartosz Golaszewski <[e-mail]>

Documentation/devicetree/bindings/gpio/gpio-pca95xx.yaml

···
               - ti,pca9536
               - ti,tca6408
               - ti,tca6416
+              - ti,tca6418
               - ti,tca6424
               - ti,tca9535
               - ti,tca9538