[pmp] Put signature and stack in last PMP entries
[pmp] Put signature and stack in last PMP entries

Except for the full random test in which case the signature and stack
stay just after the code region.
This change is necessary to not break the default configuration of PMP
entries, which rely on consecutive TOR regions.

Signed-off-by: Marno van der Maas <580d44e9051f21f57464b1cc2f7670f31c81fe23@lowrisc.org>

google/riscv-dv,google/riscv-dv,google/riscv-dv