uboot-imx

ARM: chiliboard: remove dead !CONFIG_DM_SERIAL code

DM_SERIAL is selected by TARGET_CHILIBOARD, so there is no reason to
keep code that will not be built. Remove it.

Signed-off-by: Marcin Niestroj <m.niestroj@grinn-global.com>
Reviewed-by: Tom Rini <trini@konsulko.com>