1. add kconfig help for GPIO0 output mode
2. fix a bug when select gpio0 output mode and initialize psram
3. make default config to official development board
4. fix wrong LAN8720 register index
newlib uses significantly more stack space when printing to an
unbuffered stream. To reduce the amount of stack space required to
use the console, don’t disable buffering. linenoise should support
unbuffered stdout instead.
1. Add command for Ethernet based on console component.
2. Make cmd_system and iperf a component that can be referenced by other examples
3. Add "version" command to cmd_system.c
4. Clean up the README.md in all ethernet examples[TW#26525]
