Add extensive testing

[andreaskuster]

• add extensive { access, denial } x { axi burst length, size } x { read, write } x { random offsets, lower bound, upper bound }
• test granularity / granularity extraction according to the RISCV privilege specs
• test all 16 PMP slots
• test priority of the PMPs
• add extensive boundary tests (for all power-of-two)

All these are CI-pipeline and will therefore be checked against with every push/PR.

In the process of this implementation, I changed the PMP granularity enforcement to always comply to the standard (i.e. to pass all tests)

Furthermore, I added a reg_cut module to cut the register interface path before we wire the signal into the IO-PMP