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/CMakeLists.txt b/CMakeLists.txt
index 4276cf6..d0c6ce5 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -42,7 +42,8 @@
 
 set (IPMB_SRC_FILES src/Utils.cpp src/Thresholds.cpp)
 
-set (PSU_SRC_FILES src/Utils.cpp src/PSUSensor.cpp src/Thresholds.cpp)
+set (PSU_SRC_FILES src/Utils.cpp src/PSUSensor.cpp src/Thresholds.cpp
+     src/PwmSensor.cpp)
 
 set (EXTERNAL_PACKAGES Boost sdbusplus-project nlohmann-json)
 set (SENSOR_LINK_LIBS -lsystemd stdc++fs sdbusplus)