hw/misc/tz-msc: Model TrustZone Master Security Controller

hw/misc/tz-msc: Model TrustZone Master Security Controller

Implement a model of the TrustZone Master Securtiy Controller,
as documented in the Arm CoreLink SIE-200 System IP for
Embedded TRM  (DDI0571G):
  https://developer.arm.com/products/architecture/m-profile/docs/ddi0571/g

The MSC is intended to sit in front of a device which can
be a bus master (eg a DMA controller) and programmably gate
its transactions. This allows a bus-mastering device to be
controlled by non-secure code but still restricted from
making accesses to addresses which are secure-only.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Message-id: 20180820141116.9118-12-peter.maydell@linaro.org
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>