hw/misc/tz-mpc.c: Implement the Arm TrustZone Memory Protection Controller

hw/misc/tz-mpc.c: Implement the Arm TrustZone Memory Protection Controller

Implement the Arm TrustZone Memory Protection Controller, which sits
in front of RAM and allows secure software to configure it to either
pass through or reject transactions.

We implement the MPC as a QEMU IOMMU, which will direct transactions
either through to the devices and memory behind it or to a special
"never works" AddressSpace if they are blocked.

This initial commit implements the skeleton of the device:
 * it always permits accesses
 * it doesn't implement most of the registers
 * it doesn't implement the interrupt or other behaviour
   for blocked transactions

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Eric Auger <eric.auger@redhat.com>
Message-id: 20180620132032.28865-2-peter.maydell@linaro.org