xilinx: zynq: Add support to secure images

This patch basically adds two new commands for loadig secure
images.
1. zynq rsa adds support to load secure image which can be both
   authenticated or encrypted or both authenticated and encrypted
   image in xilinx bootimage(BOOT.bin) format.
2. zynq aes command adds support to decrypt and load encrypted
   image back to DDR as per destination address. The image has
   to be encrypted using xilinx bootgen tool and to get only the
   encrypted image from tool use -split option while invoking
   bootgen.

Signed-off-by: Siva Durga Prasad Paladugu <siva.durga.paladugu@xilinx.com>
Signed-off-by: Michal Simek <michal.simek@xilinx.com>