add initial zynqmp support to the kernel-loader

[moritz-meier]

Added initial support for Xilinx ZynqMP to the sel4-kernel-loader. One current problem is missing device-tree support in the kernel-loader, that is why the base address of the serial port is currently hard-coded. Any ideas on how to solve this platform dependence?

[nspin]

Excellent, thank you.

Yes, the next step for the kernel loader is for it to not depend on CONFIG_PLAT_* at compile-time, but rather configure itself at runtime using the device tree like elfloader does. I'm not sure when I myself will get around to doing that upgrade, but I'd welcome a PR!