docs(gptimer): include etm content conditionally

https://www.esp32.com/viewtopic.php?f=12&t=40991&p=135107#p135098

components/hal/include/hal/timer_types.h

@@ -34,6 +34,7 @@ typedef enum {
     GPTIMER_COUNT_UP,   /*!< Increase count value */
 } gptimer_count_direction_t;
 
+#if SOC_TIMER_SUPPORT_ETM
 /**
  * @brief GPTimer specific tasks that supported by the ETM module
  */
@@ -53,6 +54,7 @@ typedef enum {
     GPTIMER_ETM_EVENT_ALARM_MATCH, /*!< Count value matches the alarm target value */
     GPTIMER_ETM_EVENT_MAX,         /*!< Maximum number of events */
 } gptimer_etm_event_type_t;
+#endif // SOC_TIMER_SUPPORT_ETM
 
 #ifdef __cplusplus
 }