k/mm_fault: make unprivileged faults more obvious.
k/mm_fault: make unprivileged faults more obvious.

Eventually this will become a supervisor message, but for now, halt
execution at an obvious location.  (Previously, this would go into an
infinite fault loop.)

cbiffle/brittle-kernel,cbiffle/brittle-kernel,cbiffle/brittle-kernel,cbiffle/brittle-kernel