boards: stm32f4: Extract common config options Move common config options one level up to try to simplify the per-board defconfig Change-Id: I3d80fa494050634d0f877af2015b01b85df20d1d Signed-off-by: Amit Kucheria <amit.kucheria@linaro.org> Signed-off-by: Kumar Gala <kumar.gala@linaro.org>