PINEBOOK Pro U-Boot splash screen

[Marc Baudoin <babafou%babafou.eu.org@localhost>]

Hi again,

The default U-Boot configuration of the PINEBOOK Pro (straight
from the factory) displays a PINE64 / Debian wallpaper once the
system is switched on.  I'd love to have a NetBSD wallpaper but
the actual NetBSD U-Boot configuration doesn't display anything
but an empty screen before the kernel boots.

I checked the U-Boot documentation but didn't find anything about
this.  Does anybody know how to configure the wallpaper in
U-Boot?