fs/cromfs and tools/gencromfs: Various fixes for traversal relative file...

fs/cromfs and tools/gencromfs:  Various fixes for traversal relative file paths.  Biggest changes is in types used:  Cannot use size_t or mode_t in common structures because they have different sizes on the (64-bit) host and the (32-bit) target.  Use uint32_t instead of size_t for offsets.  Use uint16_t instead of mode_t.