meta-witherspoon: Add psu.json for phosphor-power

The service psu-monitor in phosphor-power now requires psu.json to
run. Otherwise it fails due to unable to open and parse the JSON file.

Install psu.json for Witherspoon so it works OK.

Tested: On Witherspoon, the psu-monitor services are started correctly,
        and the PSU model, serial, etc are correct in inventory.

Change-Id: I3135a7f75ddd2fb68b5a05409603af6a1d6c3cac
Signed-off-by: Lei YU <mine260309@gmail.com>
2 files changed