nvme: add support for DIOCGIDENT

Add support for the DIOCGIDENT ioctl to both nvme controller device
nodes and namespace device nodes.

This information was already available via the nda(4) device node.
However, mapping /dev/nvmeX to /dev/ndaY device nodes is not
straightforward, so it's better to get it directly from the /dev/nvme
device node.

PR: 290259
Sponsored by: ConnectWise
Submitted by: imp (mostly)
Pull Request: https://github.com/freebsd/freebsd-src/pull/1875

(cherry picked from commit 6d0001d44490becdd20d627ce663c72a30b9aac3)