hw/arm/mps3r: Initial skeleton for mps3-an536 board

hw/arm/mps3r: Initial skeleton for mps3-an536 board

The AN536 is another FPGA image for the MPS3 development board. Unlike
the existing FPGA images we already model, this board uses a Cortex-R
family CPU, and it does not use any equivalent to the M-profile
"Subsystem for Embedded" SoC-equivalent that we model in hw/arm/armsse.c.
It's therefore more convenient for us to model it as a completely
separate C file.

This commit adds the basic skeleton of the board model, and the
code to create all the RAM and ROM. We assume that we're probably
going to want to add more images in future, so use the same
base class/subclass setup that mps2-tz.c uses, even though at
the moment there's only a single subclass.

Following commits will add the CPUs and the peripherals.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Message-id: 20240206132931.38376-9-peter.maydell@linaro.org