buildroot

configs: update boards to u-boot custom version option

Some board configs where left out of the u-boot custom version
migration, so do it otherwise they'll just pull the latest version which
might not work and brick the device.

Signed-off-by: Gustavo Zacarias <gustavo@zacarias.com.ar>
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>