hw/arm/armv7m: Add mpu-ns-regions and mpu-s-regions properties

M-profile CPUs generally allow configuration of the number of MPU
regions that they have.  We don't currently model this, so our
implementations of some of the board models provide CPUs with the
wrong number of regions.  RTOSes like Zephyr that hardcode the
expected number of regions may therefore not run on the model if they
are set up to run on real hardware.

Add properties mpu-ns-regions and mpu-s-regions to the ARMV7M object,
matching the ability of hardware to configure the number of Secure
and NonSecure regions separately.  Our actual CPU implementation
doesn't currently support that, and it happens that none of the MPS
boards we model set the number of regions differently for Secure vs
NonSecure, so we provide an interface to the boards and SoCs that
won't need to change if we ever do add that functionality in future,
but make it an error to configure the two properties to different
values.

(The property name on the CPU is the somewhat misnamed-for-M-profile
"pmsav7-dregion", so we don't follow that naming convention for
the properties here. The TRM doesn't say what the CPU configuration
variable names are, so we pick something, and follow the lowercase
convention we already have for properties here.)

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Message-id: 20230724174335.2150499-3-peter.maydell@linaro.org