esp_system: Fix some ESP_EARLY_LOG lines not being output fully

At least on ESP32, calling esp_rom_uart_set_clock_baudrate() causes the
contents of the UART FIFO to be discarded.

components/esp_system/port/cpu_start.c

@@ -456,6 +456,7 @@ void IRAM_ATTR call_start_cpu0(void)
 #if CONFIG_IDF_TARGET_ESP32S3 || CONFIG_IDF_TARGET_ESP32C3
     clock_hz = UART_CLK_FREQ_ROM; // From esp32-s3 on, UART clock source is selected to XTAL in ROM
 #endif
+    esp_rom_uart_tx_wait_idle(CONFIG_ESP_CONSOLE_UART_NUM);
     esp_rom_uart_set_clock_baudrate(CONFIG_ESP_CONSOLE_UART_NUM, clock_hz, CONFIG_ESP_CONSOLE_UART_BAUDRATE);
 #endif