uvm: keep track of maxrss
uvm: keep track of maxrss

The fault path is used to update the maxrss of the faulting proc.
Doesn't affect anything, as it was 0 before.

Requested by espie, "just commit it" deraadt

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