stm32: add support for stm32f7 & stm32f746 discovery board

This patch adds support for stm32f7 family & stm32f746 board.

Signed-off-by: Vikas Manocha <vikas.manocha@st.com>
diff --git a/arch/arm/mach-stm32/stm32f7/Kconfig b/arch/arm/mach-stm32/stm32f7/Kconfig
new file mode 100644
index 0000000..287e5ad
--- /dev/null
+++ b/arch/arm/mach-stm32/stm32f7/Kconfig
@@ -0,0 +1,8 @@
+if STM32F7
+
+config TARGET_STM32F746_DISCO
+	bool "STM32F746 Discovery board"
+
+source "board/st/stm32f746-disco/Kconfig"
+
+endif