Platform: Add support for MPS3 AN524 FPGA board

Details:
1. Adds AN524 platform support files
2. Adds a new target platform to the build system: "AN524"
3. Updates the docs with details for AN524

Change-Id: I7c192e951253dfc72512d73ee5da3f94023a248f
Signed-off-by: Kevin Peng <kevin.peng@arm.com>
65 files changed