The new teensy loader keeps the file system under certain conditions:
- The file size is properly set in the file header.
- The header version is 4.3
These changes are implemented here, requiring a backport of
fsl_flexspi_nor_boot.c. There is still a problem with the command line
version of the teensy loader, which fails on the first attempt. At the
second attempt it works. The GUI version of the teensy loader is fine.
