ARMv7M: add STM32F1 support

Add ARMv7M STM32F1 support including clocks, timer, gpio, and flash.

Signed-off-by: Matt Porter <mporter@konsulko.com>
diff --git a/arch/arm/cpu/armv7m/Makefile b/arch/arm/cpu/armv7m/Makefile
index b662e03..93a1956 100644
--- a/arch/arm/cpu/armv7m/Makefile
+++ b/arch/arm/cpu/armv7m/Makefile
@@ -8,4 +8,5 @@
 extra-y := start.o
 obj-y += cpu.o
 
+obj-$(CONFIG_STM32F1) += stm32f1/
 obj-$(CONFIG_STM32F4) += stm32f4/