ARM: hisilicon: hikey: Enable OF_CONTROL for hikey board.

Currently only the serial pl01x driver is using DT,
and the other drivers still use platform data but
as more DT lands in the upstream kernel the aim is
to migrate the other drivers over to DT as well to
have a fully DT configured hikey u-boot.

Signed-off-by: Peter Griffin <peter.griffin@linaro.org>
Reviewed-by: Tom Rini <trini@konsulko.com>