[U-Boot] FIT: workarounding wrong configuration name

[yegorslists at googlemail.com]

In our project we read device ID from EEPROM and then select an appropriate
configuration "bootm ${loadaddr}#conf${board_name}". If for some reason wrong
ID was written into EEPROM, then it is still important, that device can still
be booted with default configuration.

One can still put a big warning, saying, that provided configuration is missing
and that the system is using default one.

What do you think about this?

Regards,
Yegor