For compatibility with other ports. Code increase up to ~1250 bytes for
SAMD21. The feature is configurable via MICROPY_PY_MACHINE_PIN_BOARD_CPU
in case flash memory is tight.
Pin numbers are now the MCU port numbers in the range:
PA0..PA31: 0..31
PB0..PB31: 32..63
PC0..PC31: 64..95
PD0..PD31: 96..127
Pins can be denoted by the GPIO port number, the name as defined in
pins.csv or a string in the form Pxnn, like "PA16" or "PD03".
The pins.c and pins.h files are now obsolete. The pin objects are part of
the AF table.
As result of a simplification, the code now supports using pin names or
numbers instead of pin objects for modules like UART, SPI, PWM, I2C, ADC,
pininfo.
