Add PL bitstream dowload support for ZynqMP
Bitstream will be validated by uboot and loaded
to PL by invoking an smc instruction to ATF which route this request to
PMU FW which will take care of loading it to PL

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