We get odd warnings associated with Kconfig because of this:
warning: symbol value '0# empty for now, use this file for global kernel
configurations and overrides.' invalid for CLOCK_STM32F4X_APB2_PRESCALER
Change-Id: I77c2828ab29dfa179f345953cc490dbd67fd0b5a
Signed-off-by: Kumar Gala <kumar.gala@linaro.org>