GPIO: PCAL6534 expander lacks support for last 2 channels

[vbrzeski]

Is your enhancement proposal related to a problem? Please describe.
The PCAL6534 driver doesn't support the last two channels. I'd be willing to make these changes,
but its unclear how we could do so cleanly.

This caveat in particular:
https://github.com/zephyrproject-rtos/zephyr/blob/main/dts/bindings/gpio/nxp%2Cpca_series.yaml#L21-L22

Making the GPIO bitmap 64-bits wide is the "simplest" solution, but this would impact each driver in-tree.

Special-casing this type would be problematic as we'd violate the generic gpio Zephyr APIs.

Describe the solution you'd like
Its possible we can split the gpio_pcal_series into 1-4 seperate logical expanders depending on version,
but I'd like some feedback before doing so.

I need to unblock myself temporarily, but ideally we wouldn't fork Zephyr Drivers.

Describe alternatives you've considered

• Forking the driver