fpga: zynqmp: support loading encrypted bitfiles

Add supporting new compatible string "u-boot,zynqmp-fpga-enc" to
handle loading encrypted bitfiles.

This feature requires encrypted FSBL, as according to UG1085:
"The CSU automatically locks out the AES key, stored in either BBRAM
 or eFUSEs, as a key source to the AES engine if the FSBL is not
 encrypted. This prevents using the BBRAM or eFUSE as the key source
 to the AES engine during run-time applications."

Signed-off-by: Adrian Fiergolski <adrian.fiergolski@fastree3d.com>
Co-developed-by: Oleksandr Suvorov <oleksandr.suvorov@foundries.io>
Signed-off-by: Oleksandr Suvorov <oleksandr.suvorov@foundries.io>
Tested-by: Adrian Fiergolski <adrian.fiergolski@fastree3d.com>
Link: https://lore.kernel.org/r/20220722141614.297383-14-oleksandr.suvorov@foundries.io


Signed-off-by: Michal Simek <michal.simek@amd.com>