Add tests for `sfdp_parse_sector_map_table()` which currently (at the
time of this commit) supports flash devices with
* no Sector Map Parameter Table (i.e. the whole flash is uniform and
non-configurable)
* a single descriptor in the Sector Map Parameter Table (i.e. the
flash layout is non-configurable and has multiple regions)

Support and unit tests for flashes with multiple configurable layouts
will be added in the future.

Note: The implementation of `sfdp_parse_sector_map_table()` assumes
the table to be valid if read succeeds, so the SFDP reader callback
needs to ensure it reads data correctly or return an error.