This adds named-pins support to the esp32 port, following other ports.
Since the name of esp32 CPU pins is just GPIOx, where x is an integer, the
Pin.cpu dict is not supported and CPU pins are just retrieved via their
existing integer "name" (the cost of adding Pin.cpu is about 800 bytes,
mostly due to the additional qstrs).
What this commit supports is the Pin.board dict and constructing a pin by
names given by a board. These names are defined in a pins.csv file at the
board level. If no such file exists then Pin.board exists but is empty.
As part of this commit, pin and pin IRQ objects are optimised to reduce
their size in flash (by removing their gpio_num_t entry). The net change
in firmware size for this commit is about -132 bytes.
Signed-off-by: Damien George <damien@micropython.org>
Damien George