Copy head (r256279) to stable/10 as part of the 10.0-RELEASE cycle.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

FIPS 140-2 rng data tester for h/w crypto devices. This driver periodically
monitors the entropy data harvested by crypto drivers to verify it complies
with FIPS 140-2. If data fails any test then the driver discards it and
commences continuous testing of harvested data until it is deemed ok.
Results are collected in a statistics block and, optionally, reported on
the console. In normal use the overhead associated with this driver is
not noticeable.

Note that drivers must (currently) be compiled specially to enable use.

Obtained from: original code by Jason L. Wright