ACPERM/GCPERM - use of the M-bit is ambiguous

[tariqkurd-repo]

The AP field tables include the M-bit
ACPERM doesn't AND that permission bit but the rules do include clearing it if X is cleared
GCPERM doesn't return that permission

But the M-bit is encoded with the other architectural permissions, for RV32 and for RV64, in tables 3 and 4.

My proposed fix is to include the M-bit into the definition of ACPERM/GCPERM so we have a consistent definition of AP.

[tariqkurd-repo]

The M-bit isn't a permission, it can be toggled arbitrarily (providing the cap isn't sealed)

It can be cleared as a result of ACPERM, if X is removed, sort of. In fact if X=0 then it is no longer the M-bit, so it becomes non-existant - so it can change state between existant and non-existant as a result of ACPERM.

I'll tidy up the doc to remove the M-bit from the AP field. The current spec for ACPERM, GCPERM is believed correct.