Not enabled by default on any board. For a board to enable ROMFS it must:
- Add `#define MICROPY_VFS_ROM (1)` to its `mpconfigboard.h` file.
- Use `partitions-4MiB-romfs.csv` as its partitions file (or a similar
partitions definition that has an entry labelled "romfs").
Signed-off-by: Damien George <damien@micropython.org>