This commit includes the following changes:
- the default flash mode in bootloader should be dio and not dout
- the default flash configuration for ESP32 has to be exported to be also visible in cpu/esp32/bootloader/Makefile
- the comments in cpu/esp8266/Makefile.include have to be removed so that the flash configuration do not contain trailing white spaces
The former FLASH_MODE_{DOUT,DIO,QOUT,QIO} defines are replaced by the corresponding CONFIG_FLASHMODE_{DOUT,DIO,QOUT,QIO} and CONFIG_ESPTOOLPY_FLASHMODE_{DOUT,DIO,QOUT,QIO} as used by the ESP-IDF. This is also needed for the migration of defining flash mode in Kconfig.