Mark non existing HW support in Supported modules on Linux and Zephyr

[kenchris]

It would be nice to know whether the software is missing support, or the device actually lacks the hardware.

Currently blank can mean either and it is confusing

[grgustaf]

Good point. The full situation is a bit more complex:

• Sometimes there is no hardware
• Sometimes the hardware can be added (like an Ethernet module)
• Sometimes the support is minimal (like GPIOs on most platforms: works but w/o friendly pin names)
• Sometimes it should work but hasn't been tested
• Sometimes there's no support in Zephyr
• Sometimes there's no support in ZJS

We should try to expand the table in README to include all this detail.