stm32: exti: Define all irqs in common header.

There's more exti lines on many more devices now. F0 and F3 have extras, as did
L1 and L0.  There's no real reason not to have higher order EXTI definitions
defined at the top level, and it reduces the number of files to merge together
to find all definitions for the bigger devices.

Signed-off-by: Karl Palsson <karlp@tweak.net.au>

Fixes #338