Add OUTTOGGLE mode to STM32H7 timer driver (#541)

* stm32h7: New timer output mode STM32_TIM_CH_OUTTOGGLE.
In this mode timer generates a square waveform on given timer channel.
The maximal waveform freq is timer clock divided by 4 (prescaler 1, period 1 results in 2 clocks '0' and 2 clocks '1').

* stm32_tim.h styling fixes.

arch/arm/src/stm32h7/stm32_tim.c

@@ -904,6 +904,11 @@ static int stm32_tim_setchannel(FAR struct stm32_tim_dev_s *dev,
       case STM32_TIM_CH_DISABLED:
         break;
 
+      case STM32_TIM_CH_OUTTOGGLE:
+        ccmr_val  = (ATIM_CCMR_MODE_OCREFTOG << ATIM_CCMR1_OC1M_SHIFT);
+        ccer_val |= ATIM_CCER_CC1E << (channel << 2);
+        break;
+
       case STM32_TIM_CH_OUTPWM:
         ccmr_val  = (ATIM_CCMR_MODE_PWM1 << ATIM_CCMR1_OC1M_SHIFT) +
                     ATIM_CCMR1_OC1PE;

arch/arm/src/stm32h7/stm32_tim.h

@@ -137,11 +137,12 @@ typedef enum
 
   /* MODES: */
 
-  STM32_TIM_CH_MODE_MASK      = 0x06,
+  STM32_TIM_CH_MODE_MASK      = 0x0e,
 
   /* Output Compare Modes */
 
   STM32_TIM_CH_OUTPWM         = 0x04,    /* Enable standard PWM mode, active high when counter < compare */
+  STM32_TIM_CH_OUTTOGGLE      = 0x08,    /* Toggle TIM_CHx output on UEV */
 #if 0
   STM32_TIM_CH_OUTCOMPARE     = 0x06,
 
@@ -181,7 +182,7 @@ struct stm32_tim_ops_s
 };
 
 /****************************************************************************
- * Public Functions
+ * Public Function Prototypes
  ****************************************************************************/
 
 /* Power-up timer and get its structure */