gnss: limit to supported baudrates

[julianoes]

Without this change, the console is flooded with warnings like this:

WARN  [SerialImpl] Using non-standard baudrate: 500000

FYI @flyingthingsintothings

[flyingthingsintothings]

I thought about this when I wrote the driver. The problem is that these non-standard baud rates are supported on the receivers, so if the user set them before, the driver can't configure the receiver because it won't detect these non-standard baud rates. A better option would be to move all the non-standard ones at the end of the array to not print warnings if the receiver is using a standard one. Another option would be to document the non-standard baud rates in the dev docs instead of printing warnings.

[julianoes]

Alternatively, you could add the baudrates to SerialImpl and then test it, to make sure they work.

[flyingthingsintothings]

Sorry for the late reply. I was away for a week.

I'll try to add the baud rates and test with that. That seems like the cleanest, correct solution.