Currently, only the bus specs of the stm32f405xx have been coded.
Other stm-family chips need (at a minimum) the specs added in their
periph.[ch] files.
Since Actions passed on the previous commit, where this computed value
was checked against the specified value (if any), this is no net change,
except that we no longer need to specify it for particular boards or
ports.
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.
