libopencmsis: Fill in missing CMSIS interrupt links

And correct a minor typo in the generated code.
stm32/flash: Make comments match reality

Copy/paste commentary with wrong sizes.
stm32/dac: Follow ref-man guidelines on GPIO config

GPIO pins should be configured for Analog IN on virtually all families
to reduce parasitic consumption.

Reported-by: Roger Wolff <R.E.Wolff@BitWizard.nl>