Improve blisp_flash_firmware error handling:
- Address never checked return of `parse_firmware_file`
- Ensure the function always returns the correct blisp_return_t value
- Make error checking syntactic dance consistent
Move function definitions in include/blisp_util.h to lib/blisp_util.c.
Defining them as static leads to internal linkage, accessible in that
translation unit, hence the warning. Their references are to be handled
in other translation units, so they shouldn't be static.
Berk D. Demir