psu-ng: Add peak input power sensor for some PSs

Some models of the ibm-cffps power supplies support an 'input history'
command that reports 30 second maximum and average input power values.
The code was currently putting those on an 'org.open_power' D-Bus
interface so that the history of those values could be captured in a
single D-Bus call.

Now that there is a real telemetry feature in Redfish that can capture
the history of a single sensor value, we can drop the custom D-Bus
interface and just use the normal Sensor.Value interface that contains
the most recent maximum value from the input history command, The sensor
name will be 'psX_input_power_peak' where X is the PS instance number.

The average input power telemetry will now just be obtained from the
psX_input_power sensor provided by phosphor-hwmon so an equivalent
sensor to the peak isn't needed here.

This commit will add support for putting the new sensor on D-Bus, and a
future one will remove the previous input history support.

Like sensors in other daemons, it will be set to not available when a PS
is removed, and not functional when it has an access problem.  There
will be associations to the parent chassis and to the power supply so it
will show up in Redfish output with the other sensors.

This commit did remove one of the input history testcases, as trying to
get the right sequence of EXPECT_CALLs would get tricky when both the
old and new are running together.

Tested:
- New sensor shows up when PS is present and supports it.
 - All interfaces on the object path are correct.
- Sensor value matches what org.open_power Max property had.
- Works correctly when:
 - PS is missing on startup
 - PS is removed
 - Previously present PS is replaced.

Change-Id: Id9c33aa753c9af32880a0cc874b39c113222568f
Signed-off-by: Matt Spinler <spinler@us.ibm.com>
diff --git a/phosphor-power-supply/test/mock.hpp b/phosphor-power-supply/test/mock.hpp
index 6e2705e..41db263 100644
--- a/phosphor-power-supply/test/mock.hpp
+++ b/phosphor-power-supply/test/mock.hpp
@@ -61,6 +61,12 @@
                 (sdbusplus::bus_t & bus, const std::string& invpath,
                  bool addRollup),
                 (const, override));
+
+    std::string getChassis(sdbusplus::bus_t& /*bus*/,
+                           const std::string& /*invpath*/) const override
+    {
+        return "/xyz/openbmc_project/inventory/system/chassis";
+    }
 };
 
 class MockedGPIOInterface : public GPIOInterfaceBase