nvmecontrol: add device self-test op and log page

Add decoding of the Device Self-test log page and the ability to start
or abort a test.

Reviewed by: imp, mav
Tested by: Muhammad Ahmad <muhammad.ahmad@seagate.com>
MFC after: 2 weeks
Differential Revision: https://reviews.freebsd.org/D27517

(cherry picked from commit 6733401935f83754b4b2744bc3d33ef84b1271e0)