cam/scsi: Use xpt_path_inq() instead of hand-rolled expansion

Use xpt_path_inq() for all XPT_PATH_INQ requests. They all should be
CAM_PRIORITY_NONE since XPT_PATH_INQ is an unqueued command, so the
minor changes here from _NORMAL to _NONE don't matter. And the one place
we preseve the priority doesn't matter either: It's an allocated CCB,
true, but it only ever stores the CPI from XPT_PATH_INQ.

Sponsored by: Netflix
Reviewed by: jhb
Differential Revision: https://reviews.freebsd.org/D51121