uboot-phytec

rockchip: mkimage: add support for RK3308

Usage:

 (1) tools/mkimage -n rk3308 -T rksd -d tpl/u-boot-tpl.bin idbloader.img
 (2) cat spl/u-boot-spl.bin >> idbloader.img
 (3) upgrade_tool wl 0x40 idbloader.img

Note:
  When use ddr binary from rkbin as tpl, use it replace u-boot-tpl.bin in(1)

Signed-off-by: Andy Yan <andy.yan@rock-chips.com>
Reviewed-by: Kever Yang <kever.yang@rock-chips.com>