unifykey: support both old and new unifykey format

unifykey: support both old and new unifykey format

PD#148057: for m8bb m200 platform, we have the latest linux kernel
and a relative old version uboot running on it. For some historic
resons, the unifykey data stored in emmc/nand has totally different
format, which means the key stored by old uboot cannot be fetched
out by new kernel. To solve this problem, we have to support both
the old and new unifykey dataformat in lasted kernel.

Change-Id: Ic70df6543466b345a5ff513bfaabfe4cfcf647ed
Signed-off-by: Jiamin Ma <jiamin.ma@amlogic.com>