stm32f1x_cl: Add initial support for STM32F1x connectivity line

This currently supports the stm32f107, but support will be added for
the F105 shortly (missing a linker script and I can't properly test
without a devkit).

cpu/arm/stm32f1x_cl/uip-log.c

@@ -0,0 +1,7 @@
+#include <stdio.h>
+
+void
+uip_log(char *msg)
+{
+  printf("uip: %s\n", msg);
+}