Saving RAM words to Flash

[mkobetic]

The "new flash framework" allows for compiling words directly into flash. Implementation for new MCUs should require implementing few flash writing hooks and the rest should just work.

Few notes specific to RA4M1:

1. RA4M1 code flash is erased in 2K blocks and written in 8byte chunks.
2. RA4M1 doesn't allow writing into code flash with code in the code flash. So the flash writing code must be relocated into RAM and run from there.