nvmecontrol: Always build instead of being conditional on WITH_NVME

This now builds fine on all platforms so always include it similar
to other tools such as camcontrol.

Reviewed by: imp, emaste
Sponsored by: Chelsio Communications
Differential Revision: https://reviews.freebsd.org/D44842

(cherry picked from commit 2d51a9898e26c87586ba50e71b6b3fdf1591713d)