[stm32x] Use modern header include paths.

Replace includes of stm32/YY/xxxx.h with stm32/xxxx.h
Replace stm32/YY/nvic.h with cm3/nvic.h.
In some cases, the include list was resorted alphabetically when it was
complicated and I was reviewing them manually, but most of this was
automatically done.

examples/stm32/l1/stm32l-discovery/button-irq-printf-lowpower/main.c

@@ -23,14 +23,14 @@
 #include <libopencm3/cm3/nvic.h>
 #include <libopencm3/cm3/scb.h>
 #include <libopencm3/stm32/dbgmcu.h>
+#include <libopencm3/stm32/exti.h>
+#include <libopencm3/stm32/flash.h>
 #include <libopencm3/stm32/gpio.h>
 #include <libopencm3/stm32/pwr.h>
-#include <libopencm3/stm32/exti.h>
+#include <libopencm3/stm32/rcc.h>
+#include <libopencm3/stm32/rtc.h>
 #include <libopencm3/stm32/timer.h>
 #include <libopencm3/stm32/usart.h>
-#include <libopencm3/stm32/rtc.h>
-#include <libopencm3/stm32/l1/rcc.h>
-#include <libopencm3/stm32/l1/flash.h>
 
 #include "syscfg.h"
 

examples/stm32/l1/stm32l-discovery/button-irq-printf/main.c

@@ -21,7 +21,7 @@
 #include <stdio.h>
 #include <unistd.h>
 #include <libopencm3/cm3/nvic.h>
-#include <libopencm3/stm32/l1/rcc.h>
+#include <libopencm3/stm32/rcc.h>
 #include <libopencm3/stm32/gpio.h>
 #include <libopencm3/stm32/exti.h>
 #include <libopencm3/stm32/timer.h>

examples/stm32/l1/stm32l-discovery/miniblink/miniblink.c

@@ -19,8 +19,8 @@
  * along with this library.  If not, see <http://www.gnu.org/licenses/>.
  */
 
-#include <libopencm3/stm32/l1/rcc.h>
-#include <libopencm3/stm32/l1/gpio.h>
+#include <libopencm3/stm32/rcc.h>
+#include <libopencm3/stm32/gpio.h>
 
 #define PORT_LED GPIOB
 #define PIN_LED GPIO6

examples/stm32/l1/stm32l-discovery/usart/usart.c

@@ -18,8 +18,8 @@
  * along with this library.  If not, see <http://www.gnu.org/licenses/>.
  */
 
-#include <libopencm3/stm32/l1/rcc.h>
-#include <libopencm3/stm32/l1/gpio.h>
+#include <libopencm3/stm32/rcc.h>
+#include <libopencm3/stm32/gpio.h>
 #include <libopencm3/stm32/usart.h>
 
 static void clock_setup(void)