psu-ng: Add code to set ON_OFF_CONFIG

Add code that sends the appropriate ON_OFF_CONFIG mask for the power
supply power on operation.

Tested:
    Ran gtest using x86sdk
    Used simulator to change ON_OFF_CONFIG value, restarted service,
    verified ON_OFF_CONFIG changed.
    Used i2cget on hardware to change ON_OFF_CONFIG, restarted service,
    verified ON_OFF_CONFIG changed.

Signed-off-by: Brandon Wyman <bjwyman@gmail.com>
Change-Id: Ifd9d63fcd2e86a62b7358e08958b5e2dbd21db9f
diff --git a/phosphor-power-supply/psu_manager.hpp b/phosphor-power-supply/psu_manager.hpp
index a3bcae0..a9a0bd5 100644
--- a/phosphor-power-supply/psu_manager.hpp
+++ b/phosphor-power-supply/psu_manager.hpp
@@ -87,6 +87,7 @@
             powerOn = false;
         }
 
+        onOffConfig(phosphor::pmbus::ON_OFF_CONFIG_CONTROL_PIN_ONLY);
         clearFaults();
         updateInventory();
     }
@@ -100,6 +101,20 @@
     }
 
     /**
+     * Write PMBus ON_OFF_CONFIG
+     *
+     * This function will be called to cause the PMBus device driver to send the
+     * ON_OFF_CONFIG command. Takes one byte of data.
+     */
+    void onOffConfig(const uint8_t data)
+    {
+        for (auto& psu : psus)
+        {
+            psu->onOffConfig(data);
+        }
+    }
+
+    /**
      * This function will be called in various situations in order to clear
      * any fault status bits that may have been set, in order to start over
      * with a clean state. Presence changes and power state changes will want