Revert "Boardconfig: Enable U-Boot custom script"

This reverts commit 7ebf371aa2271c44ccb75068af0351328a40a6f5.
Boardconfig: Disable u-boot multiimage

Signed-off-by: zombah <zombah@gmail.com>
BoardConfig: Keep zImage kernel name

Signed-off-by: zombah <zombah@gmail.com>