Register mock EVS driver as EvsEnumeratorHw

This makes the mock driver (when loaded and running) serve as THE evs
driver for the system.  Facilitates VTS tests running, etc.
This driver should not run on a production system as it should have a
"real" driver registered instead.

Change-Id: I716f8f8226e7152521375b94013828a3aa2bb9f0
BUg: 65376941
Test: boot mojave, then 'ps -lef | grep evs'