zed: Look for NVMe DEVPATH if no ID_BUS

We tried replacing an NVMe drive using autoreplace, only
to see zed reject it with:

zed[27955]: zed_udev_monitor: /dev/nvme5n1 no devid source

This happened because ZED saw that ID_BUS was not set by udev
for the NVMe drive, and thus didn't think it was "real drive".
This commit allows NVMe drives to be autoreplaced even if
ID_BUS is not set.

Reviewed-by: Don Brady <don.brady@intel.com>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Tony Hutter <hutter2@llnl.gov>
Closes #13512
Closes #13646