Add support for STM32L0X using the generic STM32 backend. This is
quite a significant change since the L0 series uses a slightly
different flash controller. Refactor the generic backend to better
support different block sizes and the L0's register interface.
Signed-off-by: Andreas Sandberg <andreas@sandberg.pp.se>
Several STM32 chips have identical chip-specific code that has been
duplicated in different source files. Unify the F0x, F1x, and F3x to
use a single implementation.
Signed-off-by: Andreas Sandberg <andreas@sandberg.pp.se>