presence: Add gpio presence sensor

Add a gpio presence implementation of the PresenceSensor
interface.

The gpio sensor simply maps the on off state of a gpio
directly to the xyz.openbmc_project.Inventory.Item
Present property.

Change-Id: I071dd475bebb15372edb59506352746c20542eff
Signed-off-by: Brad Bishop <bradleyb@fuzziesquirrel.com>
3 files changed