esp_adc: add adc ulp mode disable enum

Prior to this commit, adc ulp is disabled by setting
adc_oneshot_unit_init_cfg_t::ulp_mode to false.

After this commit, a new enum `ADC_ULP_MODE_DISABLE` is added. So
setting `ulp_mode` to `ADC_ULP_MODE_DISABLE`, instead of `false`, to
disable the ulp mode.

docs/en/api-reference/peripherals/adc_oneshot.rst

@@ -62,7 +62,7 @@ Create an ADC Unit Handle under Normal Oneshot Mode
     adc_oneshot_unit_handle_t adc1_handle;
     adc_oneshot_unit_init_cfg_t init_config1 = {
         .unit_id = ADC_UNIT_1,
-        .ulp_mode = false,
+        .ulp_mode = ADC_ULP_MODE_DISABLE,
     };
     ESP_ERROR_CHECK(adc_oneshot_new_unit(&init_config1, &adc1_handle));