Provides indirect read and write access to the base address of the currently selected MPU region `FTSSS
| XN | Defines whether code can be executed from this region |
| AP | Defines the access permissions for this region |
| SH | Defines the Shareability domain of this region for Normal memory |
| BASE | Contains bits [31:5] of the lower inclusive limit of the selected MPU memory region. This value is zero extended to provide the base address to be checked against |