ARM: stm32: Introduce MACH_STM32H743 flag

This patch introduces the MACH_STM32H743 to make possible to only select
STM32H743 pinctrl driver

By default, all the MACH_STM32Fxxx flags will be set with STM32 defconfig.
Signed-off-by: Alexandre TORGUE <alexandre.torgue@st.com>

arch/arm/mach-stm32/Kconfig

@@ -19,3 +19,8 @@ config MACH_STM32F746
 	bool "STMicrolectronics STM32F746"
 	depends on ARCH_STM32
 	default y
+
+config MACH_STM32H743
+	bool "STMicrolectronics STM32H743"
+	depends on ARCH_STM32
+	default y