This patch takes the software SPI implementation from extmod/machine_spi.c
and moves it to a dedicated file in drivers/bus/softspi.c. This allows the
SPI driver to be used independently of the uPy runtime, making it a more
general component.
These were copied from the stm32 port (then stmhal) at the very beginning
of this port, with the anticipation that the esp8266 port would have board
definition files with a list of valid pins and their names. But that has
not been implemented and likely won't be, so remove the corresponding lines
from the Makefile.
This is to keep the top-level directory clean, to make it clear what is
core and what is a port, and to allow the repository to grow with new ports
in a sustainable way.
Damien George
Paul Sokolovsky