Pi Zero with two UARTs instead on one

[uraimo]

From the discussion for #98 , we discovered that a PiZero with Buster has two UARTs like the Pi 3/4. Right now the Zero shares all the configuration of the Pi 1, a new enum case should be added, easy to so in 2.0.0-beta, but that need to be documented for 1.x since the splitting of the original value will break user code.