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/configs/stm32f746-disco_defconfig b/configs/stm32f746-disco_defconfig
new file mode 100644
index 0000000..7cfed4a
--- /dev/null
+++ b/configs/stm32f746-disco_defconfig
@@ -0,0 +1,9 @@
+CONFIG_ARM=y
+CONFIG_STM32=y
+CONFIG_STM32F7=y
+CONFIG_TARGET_STM32F746_DISCO=y
+CONFIG_SYS_PROMPT="U-Boot > "
+CONFIG_AUTOBOOT_KEYED=y
+CONFIG_AUTOBOOT_PROMPT="Hit SPACE in %d seconds to stop autoboot.\n"
+CONFIG_AUTOBOOT_STOP_STR=" "
+# CONFIG_CMD_SETEXPR is not set