[U-Boot] [PATCH] Restore compatibility of image type IDs

[Philipp Tomsich]

Stefano,

> On 14.12.2018, at 15:04, Stefano Babic <sbabic at denx.de> wrote:
> 
> Commit a2b96ece5be146f4995d737f047e5bbb76079b8f breaks the enumeration
> of the Image Types. New image types can be appended, but they cannot be
> inserted in the list else backward compatibility is broken.
> This restores the images types as before 2018.11 and move i.MX8 related
> images at the end.

Adding a clearer indication than the "Do not change values for backward
compatibility” (it might not be apparent to the casual reader that this refers
to integer value assigned to enum entries) in the comment above the enum
that this to be understood as “append-only” might avoid future issues.

Thanks,
Philipp.