ulp-riscv: add support for using ADC as well as an example show-casing it.

components/ulp/ulp_riscv/include/ulp_riscv_adc.h

@@ -0,0 +1,29 @@
+/*
+ * SPDX-FileCopyrightText: 2022 Espressif Systems (Shanghai) CO LTD
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+#pragma once
+
+#include "hal/adc_types.h"
+#include "esp_err.h"
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+typedef struct {
+    adc_unit_t adc_n;       // ADC Unit
+    adc_channel_t channel;  // ADC channel
+    adc_atten_t atten;      // ADC channel attenuation
+    adc_bits_width_t width; // ADC bit width, only used for ADC unit 1
+} ulp_riscv_adc_cfg_t;      // ULP Riscv ADC configuration parameters
+
+/**
+ * @brief Initialize and calibrate the ADC for use by ULP RISCV
+ *
+ * @param cfg           Configuration parameters
+ * @return esp_err_t    ESP_OK for successful.
+ */
+esp_err_t ulp_riscv_adc_init(const ulp_riscv_adc_cfg_t *cfg);