adc_ll_digi_set_convert_mode() function

ESP32 only support ADC1 single mode. For `data_sar_sel` register: 1: [15] unit, [14:11] channel, [10:0] data, 11-bit-width at most. Only work under `ADC_LL_DIGI_CONV_BOTH_UNIT` or `ADC_LL_DIGI_CONV_ALTER_UNIT` mode. 0: [15:12] channel, [11:0] data, 12-bit-width at most. Only work under `ADC_LL_DIGI_CONV_ONLY_ADC1` or `ADC_LL_DIGI_CONV_ONLY_ADC2` mode