I discussed with Hierophect on Discord about how to "de-nest" the code
for configuring SPI objects on STM, because the problems with one
nesting level per pin becomes unmanageable with the up to 10 pins of
SDIO.
This code (which is only compile-tested so far) demonstrates the concept
we discussed.
The SCK pin is always required. Loop over all possibilities of the SCK
pin. When we are considering a particular item in the mcu_spi_sck_list
we have now become committed to using a particular periph_index. If all
the other pins can be satisfied by that periph_index, then we have a
working combination. Once we have a working combination that is not
reserved, we can return that combination. On reaching the end, we have
checked all the possible possibilities and can give the same errors as
before: One if there was a possibility that worked but was reserved;
and another if no possibility worked.
Restructures the STM port of Circuitpython to be more generic about the STM32 chip lines to support
the F7 and H7 series of chips. Adds the new Packages directory to organize different chip layouts
between lines. Makes general changes to the Makefile to condense board-level flags to the minimum
and support the new chip series. Adds the new chip line to the Peripherals directory, along with
new python tools used to generate peripheral text automatically in the tools/ directory.
