* Add CONFIG_SYSTEM_RAMDISK_SUPPORT to support system's ramdisk
* Normal boot: cmdline to bypass ramdisk in boot.img,
  but use Recovery boot: Use the ramdisk in boot.img
* commandline is larger than 512, system can't bootup sometime for commandline issue.
* support fastboot getvar.
* Support "fastboot erase" command for emmc device.
  TODO: uboot community have api to operate flash, we can unify this part
* support "fastboot flash" even on damaged gpt

Change-Id: I080c25d6569d6cab56ff025601cd3b8df21cf3dd