Currently port usage is hard-coded to the default port layout, cli
commands are coming in a future commit.
This decouples all code from the global 'serialPorts' structure which
has been removed. Any code that needs to use a serial port can use
findOpenSerialPort() and openSerialPort() and maintain it's own
reference to the port.
Ports can switch between functions. e.g. by default
cli/msp/telemetry/gps
passthrough all use USART1. Each port maintains it's current function.
see begin/endSerialPortFunction.
There are only certain combinations of serial port functions that are
supported, these are listed in serialPortFunctionScenario_e.
This commit also adds a few 'static' keywords to variables that should
have been.
There a a few other minor fixes and tweaks to various bits of code that
this uncovered too.
