delete binaries which can be built by make
define RAM as 1GiB
make "boot from USB" work

XXX THIS IS VERY DIRTY HACK! XXX

this only works with latest rkflashtool from
 https://github.com/linux-rockchip/rkflashtool

e.g.)
 rkflashtool M 0x62000000 0x1000000 < ramdisk.img
 rkflashtool M 0x63000000 0x1000000 < kernel.img
 rkflashtool M 0x64000000 0x1000000 < parameter.img
 rkflashtool B 0x63000000 0x64000000

protocol may be incompatible with Rockchip. it may be changed in future.

you may omit rkcrc header from ramdisk and/or parameter.

if you omit rkcrc header from kernel, it will not be relocated to the
load address described in KERNEL_IMG: line in parameter. (i.e. kernel
needs to be coded to start at 0x63000000 in above case)
enable "reboot to maskrom"
support non-standard reset flag

e.g.
 $ rkflashtool b 0xf6 # reboot to fastboot mode
support NAND