camcontrol: Enable WITH_NVME unconditionally

MK_NVME is no longer marked broken for any platforms, so just include
support for it always as we do for ATA and SCSI.

Reviewed by: emaste
Sponsored by: Chelsio Communications
Differential Revision: https://reviews.freebsd.org/D44841

(cherry picked from commit 2b676a66c00af03e4b64d072658d2478dbdf0a97)