STM32H7: Support the RNG Peripheral

The random number generator on the STM32H7 is identical to the v1 RNG
already present in the library. So use that, and make sure that the RCC
knows about the peripheral.

Originally filed at: https://github.com/libopencm3/libopencm3/pull/1244

Reviewed-by: Karl Palsson <karlp@tweak.net.au>
 * whitespace changes from review

include/libopencm3/stm32/h7/rcc.h

@@ -394,6 +394,7 @@ LGPL License Terms @ref lgpl_license
 #define RCC_D2CCIP2R_CECSEL_SHIFT           22
 #define RCC_D2CCIP2R_USBSEL_SHIFT           20
 #define RCC_D2CCIP2R_I2C123SEL_SHIFT        12
+#define RCC_D2CCIP2R_RNGSEL_MASK            0x3
 #define RCC_D2CCIP2R_RNGSEL_SHIFT           8
 #define RCC_D2CCIP2R_USART16SEL_SHIFT       3
 #define RCC_D2CCIP2R_USART234578SEL_SHIFT   0
@@ -402,6 +403,10 @@ LGPL License Terms @ref lgpl_license
 /** @defgroup rcc_d2ccip2r_values RCC_D2CCIP2R Values
  * @ingroup rcc_registers
  * @{*/
+#define RCC_D2CCIP2R_RNGSEL_HSI48           0
+#define RCC_D2CCIP2R_RNGSEL_PLL1Q           1
+#define RCC_D2CCIP2R_RNGSEL_LSE             2
+#define RCC_D2CCIP2R_RNGSEL_LSI             3
 #define RCC_D2CCIP2R_USART16SEL_PCLK2       0
 #define RCC_D2CCIP2R_USART234578SEL_PCLK1   0
 #define RCC_D2CCIP2R_USARTSEL_PLL2Q         1
@@ -774,6 +779,12 @@ void rcc_set_spi123_clksel(uint8_t clksel);
  */
 void rcc_set_spi45_clksel(uint8_t clksel);
 
+/**
+ * Set the clock select for the RNG device.
+ * @param[in] clksel  Clock source to configure for. @ref rcc_d2ccip2r_values
+ * @sa rcc_set_peripheral_clk_sel for equivalent generic functionality
+ */
+void rcc_set_rng_clksel(uint8_t clksel);
 
 END_DECLS
 /**@}*/

include/libopencm3/stm32/h7/rng.h

@@ -0,0 +1,23 @@
+/*
+ * This file is part of the libopencm3 project.
+ *
+ * This library is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Lesser General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public License
+ * along with this library.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#ifndef LIBOPENCM3_RNG_H
+#define LIBOPENCM3_RNG_H
+
+#include <libopencm3/stm32/common/rng_common_v1.h>
+
+#endif

include/libopencm3/stm32/rng.h

@@ -26,6 +26,8 @@
 #       include <libopencm3/stm32/f4/rng.h>
 #elif defined(STM32F7)
 #       include <libopencm3/stm32/f7/rng.h>
+#elif defined(STM32H7)
+#       include <libopencm3/stm32/h7/rng.h>
 #elif defined(STM32L0)
 #       include <libopencm3/stm32/l0/rng.h>
 #elif defined(STM32L4)