stm32: Initial support for stm32f2 (#3001)

Initial support for stm32f2 in general and STM32F207 in particular.

Boots up and communicates on STM32F207VC.

Signed-off-by: Boleslaw Ciesielski <combolek@users.noreply.github.com>

src/stm32/internal.h

@@ -8,6 +8,8 @@
 #include "stm32f0xx.h"
 #elif CONFIG_MACH_STM32F1
 #include "stm32f1xx.h"
+#elif CONFIG_MACH_STM32F2
+#include "stm32f2xx.h"
 #elif CONFIG_MACH_STM32F4
 #include "stm32f4xx.h"
 #endif