Fix filesystem/files getting erased by asset scratch space

[TinyCircuits]

See https://github.com/TinyCircuits/TinyCircuits-Tiny-Game-Engine/issues/66

This will hopefully solve the filesystem issues that randomly occur (why are they random? not sure....)

• [x] Move scratch space to start of flash after a reasonable size for the firmware
• [X] Add build check to ensure that if the firmware image does grow too large, a descriptive error is provided about overlapping regions
• [x] Add check for when more than 2MiB of assets are loaded and will start erasing filesystem (make sure the filesystem is never erased!!)