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/Makefile b/arch/arm/mach-stm32/Makefile
index ea06034..ffc537f 100644
--- a/arch/arm/mach-stm32/Makefile
+++ b/arch/arm/mach-stm32/Makefile
@@ -7,3 +7,4 @@
 
 obj-$(CONFIG_STM32F1) += stm32f1/
 obj-$(CONFIG_STM32F4) += stm32f4/
+obj-$(CONFIG_STM32F7) += stm32f7/