config: mx6_cubox-i: If we set serverip boot to the net

It is safe to assumet that if serverip is set that we should
jump right to a netboot.  Otherwise the only way to netboot is
to remove all other kernels etc from the boot directory.
config: cubox-i: Fix board detection despite u-boot's stupidity

U-Boot has great config variables like DISPLAY_BOARD_CONFIG, which
says to me, do you want to output the board config.  What it really
means is INITIALIZE_ENV_BOARD_CONFIG.  I guess they feel if you
can't output something to the console you may as well not set
any of the variables.