Port GPB is the high byte, GPA the low byte.
The lower three address bits can be configured: 0100abc.
Notice that you can specify multiple pins at the same time for functions
with argument type Pins, either by ORing the according pins, or
converting a 16bit value using the Pins(uint16_t) converting constructor.
Other functions with argument type Pin can only take one pin.
If you want to operate on all 16bit, use the get(Inputs|Outputs|Directions|Polarities)()