rmt: expose private API to get channel ID

Closes https://github.com/espressif/esp-idf/issues/10596

components/driver/include/esp_private/rmt.h

@@ -0,0 +1,33 @@
+/*
+ * SPDX-FileCopyrightText: 2023 Espressif Systems (Shanghai) CO LTD
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+// DO NOT USE THESE APIS IN YOUR APPLICATIONS
+// The following APIs are for internal test.
+
+#pragma once
+
+#include "esp_err.h"
+#include "driver/rmt_types.h"
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+/**
+ * @brief Get the unique ID of RMT channel
+ *
+ * @param[in] channel RMT generic channel that created by `rmt_new_tx_channel()` or `rmt_new_rx_channel()`
+ * @param[out] ret_id The unique ID of RMT channel
+ * @return
+ *      - ESP_OK: Get RMT channel ID successfully
+ *      - ESP_ERR_INVALID_ARG: Get RMT channel ID failed because of invalid argument
+ *      - ESP_FAIL: Get RMT channel ID failed because of other reasons
+ */
+esp_err_t rmt_get_channel_id(rmt_channel_handle_t channel, int *ret_id);
+
+#ifdef __cplusplus
+}
+#endif