Validate user power cap changes fall within limits

Add validation of the user power cap when changed via Redfish or during
boot.  Validation also needs to ensure the correct power types are being
compared (input/AC vs output/DC).

Verified on hardware with limits set via GUI and Redfish.

Change-Id: Ic0d8ce2df6fdb803bbede7e42f10f34c142c6b07
Signed-off-by: Chris Cain <cjcain@us.ibm.com>
2 files changed