stm32h7: Initial introduction into libopencm3.

Updates to a base set of includes to map to the h7 include files which are
mainly based on the f7 versions for simple devices (e.g. SPI, USART, GPIO).

Custom files that have been implemented from the datasheet/ref manual include
the memory map, RCC, PWR definitions, and irq.json file for generation of
nvic files for interrupt mapping.

Additional functionality, especially PLL and tweaks for non-F7 compatible
implementations coming in future commits.

Added documentation tree configuration.

Reviewed-by: Karl Palsson <karlp@tweak.net.au>
Changed dmaX_streamX to dmaX_strX in a few places for consistency

lib/stm32/h7/rcc.c

@@ -0,0 +1,21 @@
+/** @defgroup rcc_file RCC peripheral API
+ *
+ * @ingroup peripheral_apis
+ * This library supports the Reset and Clock Control System in the STM32 series
+ * of ARM Cortex Microcontrollers by ST Microelectronics.
+ *
+ * LGPL License Terms @ref lgpl_license
+ */
+
+#include <libopencm3/cm3/assert.h>
+#include <libopencm3/stm32/rcc.h>
+#include <libopencm3/stm32/pwr.h>
+#include <libopencm3/stm32/flash.h>
+
+/**@{*/
+
+uint32_t rcc_ahb_frequency = 64000000;
+uint32_t rcc_apb1_frequency = 64000000;
+uint32_t rcc_apb2_frequency = 64000000;
+
+/**@}*/