
Map .rodata and the KVA range corresponding to the ISA hole as NX on amd64
processors that support NX.

Tested on amd64 machines with and without NX capability.

Additional NX ranges can be added as desired to the table defined by
this diff.

ok deraadt@

orumin/openbsd-efivars,orumin/openbsd-efivars,orumin/openbsd-efivars,orumin/openbsd-efivars