uboot-config: check UBOOT_CONFIG variable, not flags, for error conditions
Sometimes there's a need to change existing UBOOT_CONFIG setting from a recipe,
distro or local config, such as an override or even switch back to UBOOT_MACHINE.
Unfortunately, there's no easy way to override or unset flags, so using them as
an error condition is rather heavy-handed. Change those conditions to check the
UBOOT_CONFIG variable itself, not its flags.
Signed-off-by: Denys Dmytriyenko <denys@ti.com> Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
