Merge branch '2022-10-31-vbe-implement-the-full-firmware-flow'

To quote Simon:
This series provides an implementation of VBE from TPL through to U-Boot
proper, using VBE to load the relevant firmware stages. It buils a single
image.bin file containing all the phases:

   TPL - initial phase, loads VPL using binman symbols
   VPL - main firmware phase, loads SPL using VBE parameters
   SPL - loads U-Boot proper using VBE parameters
   U-Boot - final firmware phase, where OS booting is processed

This series does not include the OS-booting phase. That will be the
subject of a future series.

The implementation is entirely handled by sandbox. It should be possible
to enable this on a real board without much effort, but that is also the
subject of a future series.