Swift: Put in avsbus-enable

As on Witherspoon, some VRMs on Swift need their AVS buses enabled
as part of the power on sequence.  The AVS bus connects those VRMs
to the processors so the processors can set voltages.

On Witherspoon, the sequence was
1. Disable the AVS bus
2. Manually set VRM voltages
3. Enable AVS bus

Currently on Swift there is no need to manually set voltages, so
the AVS bus disable service and script isn't required.

Tested:  Tested on swift, and ensured both witherspoon and
         witherspoon-128 still have all avs scripts and
         services installed.

Signed-off-by: Matt Spinler <spinler@us.ibm.com>
Change-Id: Icc00b16f7fca6d1163d2bb161ffd01b03b28b408
7 files changed