hSPMP clarifications

[josecm]

This PR clarifies a few points regarding the hSPMP:

• Behavior of hspmpdeleg.pmpnum when mpmpdeleg.pmpnum + hspmpdeleg.pmpnum is set to a value larger than the available number of PMP entries (hSPMP Permission Encodings #65);
• hSPMP behavior for the shadow stack encoded regions for VS/VU accesses (What happens if mpmpdeleg.pmpnum is written such that mpmpdeleg.pmpnum + hspmpdeleg.pmpnum > #implemented PMP entries? #64);
• Delegation extension dependency on the vSPMP;