Add -s (serial) and -p (physpath) to diskinfo

Return the bare requested information, intended for scripting.

The serial number of a SAS/SCSI device can be returned with
'camcontrol inquiry disk -S', but there is no similar switch for SATA.

This provides a way to get this information from both SAS and SATA disks

the -s and -p flags are mutually exclusive, and cannot be used with any
other flags.

Reviewed by: rpokala, wblock
MFC after: 1 month
Sponsored by: ScaleEngine Inc.
Differential Revision: https://reviews.freebsd.org/D7828