ARMv7M: Add STM32F4 support

Signed-off-by: Kamil Lulko <rev13@wp.pl>
Reviewed-by: Tom Rini <trini@konsulko.com>
diff --git a/arch/arm/cpu/armv7m/Makefile b/arch/arm/cpu/armv7m/Makefile
index aff60e8..b662e03 100644
--- a/arch/arm/cpu/armv7m/Makefile
+++ b/arch/arm/cpu/armv7m/Makefile
@@ -7,3 +7,5 @@
 
 extra-y := start.o
 obj-y += cpu.o
+
+obj-$(CONFIG_STM32F4) += stm32f4/