Choose a better order for the flash image / offsets

[mithro]

BTW It would be much better for these to be ordered,

• Emulator
• DTS
• Kernel
• Root FS

Emulator + DTS could be needed for non-Linux applications / operating systems. Both should be pretty small / constant size.

The RootFS is the one which is most likely to be variable in size so should be at the one at end.

Probably should also add constants for MAX_SIZE here?

_Originally posted by @mithro in https://github.com/render_node/MDExOlB1bGxSZXF1ZXN0Mzc3MTI2MDA2/pull_requests/unread_timeline