s7: support onboot sign [1/1]

PD#SWPL-171076

Problem:
Samsung need split ddr out of bl2

Solution:
add on boot sign support

Verify:
local

Change-Id: I2bda8cd1662a115344e6195ede0ff69ee58aaae8
Signed-off-by: Zhongfu Luo <zhongfu.luo@amlogic.com>
Signed-off-by: Tao Zeng <tao.zeng@amlogic.com>
6 files changed