ARM: Kconfig: Introduce MACH_STM32F429 flag

This patch introduces the MACH_STM32F429 to make possible to only select
STM32F429 pinctrl driver.

By default, all the MACH_STM32Fxxx flags will be set with STM32 defconfig.
Acked-by: NPatrice Chotard <patrice.chotard@st.com>
Acked-by: NLinus Walleij <linux.walleij@linaro.org>
Signed-off-by: NMaxime Coquelin <mcoquelin.stm32@gmail.com>

arch/arm/Kconfig

@@ -883,6 +883,11 @@ config ARCH_STM32
 	help
 	  Support for STMicroelectronics STM32 processors.
 
+config MACH_STM32F429
+	bool "STMicrolectronics STM32F429"
+	depends on ARCH_STM32
+	default y
+
 # Definitions to make life easier
 config ARCH_ACORN
 	bool