stm32:rng: f4 rng peripheral is common with at least f2

Pull it up as common code immediately. Rename to v1, extract to common
with a doxygen marker stubs, add to F2 makefiles.

include/libopencm3/stm32/common/rng_common_v1.h

@@ -25,8 +25,8 @@ specific memorymap.h header before including this header file.*/
 /** @cond */
 #ifdef LIBOPENCM3_RNG_H
 /** @endcond */
-#ifndef LIBOPENCM3_RNG_COMMON_F24_H
-#define LIBOPENCM3_RNG_COMMON_F24_H
+#ifndef LIBOPENCM3_RNG_V1_H
+#define LIBOPENCM3_RNG_V1_H
 
 /**@{*/
 
@@ -80,7 +80,7 @@ END_DECLS
 #endif
 /** @cond */
 #else
-#warning "rng_common_f24.h should not be included explicitly, only via rng.h"
+#warning "rng_common_v1.h should not be included explicitly, only via rng.h"
 #endif
 /** @endcond */
 

include/libopencm3/stm32/f2/rng.h

@@ -18,6 +18,6 @@
 #ifndef LIBOPENCM3_RNG_H
 #define LIBOPENCM3_RNG_H
 
-#include <libopencm3/stm32/common/rng_common_f24.h>
+#include <libopencm3/stm32/common/rng_common_v1.h>
 
 #endif

include/libopencm3/stm32/f4/rng.h

@@ -18,6 +18,6 @@
 #ifndef LIBOPENCM3_RNG_H
 #define LIBOPENCM3_RNG_H
 
-#include <libopencm3/stm32/common/rng_common_f24.h>
+#include <libopencm3/stm32/common/rng_common_v1.h>
 
 #endif

include/libopencm3/stm32/rng.h

@@ -20,7 +20,9 @@
 #include <libopencm3/cm3/common.h>
 #include <libopencm3/stm32/memorymap.h>
 
-#if defined(STM32F4)
+#if defined(STM32F2)
+#       include <libopencm3/stm32/f2/rng.h>
+#elif defined(STM32F4)
 #       include <libopencm3/stm32/f4/rng.h>
 #else
 #       error "stm32 family not defined."