Only applied to STM32 doc trees at present.
Instead of declaring a group for "STM32blah" in the doc-blah.h files,
and then trying to put all the common+specific peripheral code into
those groups, (which is what led to the stub doxygen holder empty .c
files) Just use a standard name like "Peripheral APIS" and place
everything into that.
Demonstrated by converting ADC and USART peripherals, which is
definitely not complete, but it shows how to make things less magical,
and less prone to copy/paste errors. Now, you can copy/paste and it
will do the right thing, because everyone uses the same group names.
This is also how to unify the mix of "STM32blah->Periphblah" and _also_
the dangling "periph_file" modules in doxygen, it merges them together
properly, as they're intended to be really.
It was never complete, even for F1 family code, and went on to be even
less complete for f0 and f3. The usefulness of a library function to
check for both the irq being enabled _and_ the status flag is highly
questionable, and caused known user confusion.
The existing, much simpler, and fully functional usart_get_flag() is
a good replacement in almost all sane use cases.
Fixes https://github.com/libopencm3/libopencm3/issues/734
