esp8266: Vendor SDK 2.0.0 over clean flash leads to bootloop

Now confirmed - flashing a firmware after esptool.py erase_flash leads to a bootloop. That means that Espressif removed automatic initialization of default system params, and now esp_init_data_default.bin needs to be flashed explicitly (at flash_end -0x4000). After it's flashed, it boots ok. Also boots ok after flashing 2.0.0 firmware over 1.5.4 firmware (assuming it already run).