rmt_tx_register_event_callbacks() function

- ESP_OK: Set event callbacks successfully - ESP_ERR_INVALID_ARG: Set event callbacks failed because of invalid argument - ESP_FAIL: Set event callbacks failed because of other error

User can deregister a previously registered callback by calling this function and setting the callback member in the `cbs` structure to NULL. When CONFIG_RMT_ISR_IRAM_SAFE is enabled, the callback itself and functions called by it should be placed in IRAM. The variables used in the function should be in the SRAM as well. The `user_data` should also reside in SRAM.