hw/arm/musca: Add MPCs

hw/arm/musca: Add MPCs

The Musca board puts its SRAM and flash behind TrustZone
Memory Protection Controllers (MPCs). Each MPC sits between
the CPU and the RAM/flash, and also has a set of memory mapped
control registers. Wire up the MPCs, and the memory behind them.
For the moment we implement the flash as simple ROM, which
cannot be reprogrammed by the guest.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>