Make the map match the reality, the current binding text is
nonsense:
- The clock required for the clocking of the serial port
must come first and is not optional (as the driver will
otherwise proceed to grab and use the apb_pclk as uartclk),
and the apb_pclk that clocks the logic must come second
as the code will retrieve the first clock by index,
whereas the PrimeCell but will explicitly look for
"apb_pclk" so this can be specified later, as it is
looked up by name.
- The pin control state "default" is the only mandated
state, the sleep state is entirely optional.
We also add an example to avoid further confusion.