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.
Prior to this patch, storage.c was a combination of code that handled
either internal flash or external SPI flash and exposed one of them as a
block device for the local storage. It was also exposed to the USB MSC.
This patch splits out the flash and SPI code to separate files, which each
provide a general block-device interface (at the C level). Then storage.c
just picks one of them to use as the local storage medium. The aim of this
factoring is to allow to add new block devices in the future and allow for
easier configurability.
Which Wiznet chip to use is a compile-time option: MICROPY_PY_WIZNET5K
should be set to either 5200 or 5500 to support either one of these
Ethernet chips. The driver is called network.WIZNET5K in both cases.
Note that this commit introduces a breaking-change at the build level
because previously the valid values for MICROPY_PY_WIZNET5K were 0 and 1
but now they are 0, 5200 and 5500.
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.
