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/test/mock.hpp b/phosphor-power-supply/test/mock.hpp
index 0c64e00..c4c2c9d 100644
--- a/phosphor-power-supply/test/mock.hpp
+++ b/phosphor-power-supply/test/mock.hpp
@@ -17,6 +17,9 @@
 
     MOCK_METHOD(uint64_t, read, (const std::string& name, Type type),
                 (override));
+    MOCK_METHOD(void, writeBinary,
+                (const std::string& name, std::vector<uint8_t> data, Type type),
+                (override));
 };
 } // namespace pmbus