Add PSU PWM sensor to support FSC

Add PSU PWM sensor to allow FSC control PSU fan pwm.

Tested:
Change property Target to 100 in dbus interface xyz.openbmc_project.Control.FanPwm
path /xyz/openbmc_project/control/fanpwm/Pwm_PSU1_Fan_1, the value in
/sys/class/hwmon/hwmonx/fan1_target also become 100, and value property in interface
/xyz/openbmc_project/sensors/fan_pwm/Pwm_PSU1_Fan_1 become 39.2157

Run ipmitool sensor list, bellow sensors will show like:
Pwm PSU1 Fan 1   | 39.200     | unspecified | ok    | na        | na        | na        | na        | na        | na
Pwm PSU2 Fan 1   | 0.000      | unspecified | ok    | na        | na        | na        | na        | na        | na

Signed-off-by: Cheng C Yang <cheng.c.yang@linux.intel.com>
Change-Id: I6a4d50912a190297dbcf4a4e5c511607f71cb0c0
diff --git a/src/PwmSensor.cpp b/src/PwmSensor.cpp
index b157d52..6402ad0 100644
--- a/src/PwmSensor.cpp
+++ b/src/PwmSensor.cpp
@@ -24,15 +24,12 @@
 static constexpr size_t pwmMax = 255;
 static constexpr size_t pwmMin = 0;
 
-PwmSensor::PwmSensor(const std::string& sysPath,
+PwmSensor::PwmSensor(const std::string& name, const std::string& sysPath,
                      sdbusplus::asio::object_server& objectServer,
                      const std::string& sensorConfiguration) :
-    sysPath(sysPath),
-    objectServer(objectServer)
+    name(name),
+    sysPath(sysPath), objectServer(objectServer)
 {
-    // strip off index from path
-    name = "Pwm_" + sysPath.substr(sysPath.find_last_of("pwm") + 1);
-
     // add interface under sensor and Control.FanPwm as Control is used
     // in obmc project, also add sensor so it can be viewed as a sensor
     sensorInterface = objectServer.add_interface(