stm32: crs: fix doxygen

We need per device header includes to make the per target documentation
generation work properly.  The dispatch headers are to dispatch to the
_target_ not directly to the final implementation, remember, the final
required headers for each may be multiple files, plus extra definitions!

include/libopencm3/stm32/l0/crs.h

@@ -0,0 +1,12 @@
+/** @defgroup crs_defines CRS Defines
+ *
+ * @brief <b>Defined Constants and Types for the Clock Recovery System.</b>
+ *
+ * @ingroup STM32L0xx_defines
+ *
+ *LGPL License Terms @ref lgpl_license
+ */
+
+#pragma once
+
+#include <libopencm3/stm32/common/crs_common_all.h>