[Bug] Set max-firmware-size in EV3 to match u-boot.

[laurensvalk]

Describe the bug
u-boot reads a fixed amount of space, but there isn't currently a check that our firmware isn't bigger than that.

Expected behavior
We should set max-firmware-size in the metadata to reflect this, so we'll get an appropriate warning if the firmware is bigger.

Alternatives
Make u-boot read exactly as much as needed by inspecting data in the image.

[dlech]

First, it would be nice to try to finalize what the actual flash memory layout is going to be. I think some of this has be brought up before, but I couldn't find it (I didn't try very hard).

• How much room is reserved for firmware?
• Are builtin sounds and images going to be part of the firmware or a separate "partition" that can be updated separately?
• How much is reserved for a user file system?

Then we can consider if the existing metadata is the right place for this or if we need something new. It could make sense to have a separate file for external flash memory layout info since not all hubs have that.

[laurensvalk]

Good points.

I think we have another 256kb to grow before we exceed the limit, so we should be fine for the foreseeable future 😄