Enable uLoader verification of the barebox bootloader.

To allow testing on devices which are not OTP-secured yet, a config flag
CONFIG_FORCE_BAREBOX_AUTH is available which overrides the 'is secure boot'
check.

Also removed the test_signed_barebox command, because its not really needed.

Change-Id: I8b179953bfb668f6c14102782512232679e4169e
9 files changed