Kconfig: add simple support for non-standard clock configuration
Kconfig: add simple support for non-standard clock configuration

Add CONFIG_CHIP_STM32F4_RCC_AHB_HZ option, visible only when
CONFIG_CHIP_STM32F4_RCC_STANDARD_CLOCK_CONFIGURATION_ENABLE option is
not selected.
CezaryGapinski/distortos,jasmin-j/distortos,CezaryGapinski/distortos,jasmin-j/distortos,CezaryGapinski/distortos,DISTORTEC/distortos,CezaryGapinski/distortos,jasmin-j/distortos,DISTORTEC/distortos,jasmin-j/distortos,DISTORTEC/distortos,DISTORTEC/distortos,CezaryGapinski/distortos,jasmin-j/distortos