sensor SDRs: lookup Board to set IPMI info

Looks up the board object, if there is an association, and if that board
object specifies an EntityId or EntityInstance, it will use those values
in the SDR.  If the configuration of the sensor also implements one or
both of those properties, then those are used instead.

Tested: Validated if the json Board file has EntityId and
EntityInstance, those values are used in the SDR.  Validated if the
configuration for the sensor has those values, then those are used
instead.  Verified it works in cases where these values are not set,
etc.

Signed-off-by: Patrick Venture <venture@google.com>
Change-Id: I998eff9b0145ede7b386041b35f488fa6dd6714f
3 files changed