docs(maintainers): add maintainers for AMD-Xilinx

Add following as maintainers for AMD Xilinx Platform ports
for TF-A Tests
- Michal Simek
- Amit Nagal
- Akshay Belsare

Signed-off-by: Akshay Belsare <akshay.belsare@amd.com>
Change-Id: I796fde094544c53d2fc6e6b6083b0687a152f276
1 file changed