add chromeos scripts

make.sh:
1.run './make.sh evb' to build evb_rk808 kernel image
2.modify 'export CROSS_COMPILE=...' to use your own toolchains,
	when trying to build outside chroot environment
3.modify 'DTB=...' to specify your own dtb

flash.sh:
run './flash.sh' to flash kernel.img

save_config.sh:
run './save_config.sh' to save current '.config'

Change-Id: I830f59024051bb3c3097e1fc69fa3441b20f0bc3