fpga: zynqmp: support loading encrypted bitfiles

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 <[email protected]>
Co-developed-by: Oleksandr Suvorov <[email protected]>
Signed-off-by: Oleksandr Suvorov <[email protected]>
Tested-by: Adrian Fiergolski <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Michal Simek <[email protected]>