rockchip: rk3399: Weaken dependency on SPL serial

Allow to disable serial console in SPL. Weak dependency is already used
with TPL serial.

Signed-off-by: Daniel Semkowicz <dse@thaumatec.com>
Reviewed-by: Quentin Schulz <quentin.schulz@cherry.de>
Reviewed-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Kever Yang <kever.yang@rock-chips.com>
1 file changed