control: Support target_path option in configuration file

The target path containing the interface
xyz.openbmc_project.control.FanPwm or
xyz.openbmc_project.control.FanSpeed can be different between
phosphor-hwmon and dbus-sensor.

In phosphor-hwmon, it is "/xyz/openbmc_project/sensors/fan_tach/".
In dbus-sensor, it is "/xyz/openbmc_project/control/fanpwm/"

This commit supports making this path configurable via "target_path".
By default, it is "/xyz/openbmc_project/sensors/fan_tach/".

Signed-off-by: Chau Ly <chaul@amperecomputing.com>
Change-Id: Id799986ff69455b7c7054070ed2ab3b2e2500a6c
diff --git a/control/example/fans.yaml b/control/example/fans.yaml
index 2583256..206206c 100644
--- a/control/example/fans.yaml
+++ b/control/example/fans.yaml
@@ -11,6 +11,10 @@
 #   sensors: [The list of sensors for this fan]
 #   target_interface: [The interface implemented by the fan target.
 #                      Default is xyz.openbmc_project.Control.FanSpeed]
+#   target_path: [The relative target path, which implements
+#                 xyz.openbmc_project.Control.FanSpeed or
+#                 xyz.openbmc_project.Control.FanPwm interface.
+#                 Default is /xyz/openbmc_project/sensors/fan_tach/]
 
 #The cooling zone, a number, and the cooling profile, a string,
 #have to match the corresponding values in the fan zone yaml
@@ -30,3 +34,4 @@
 #    sensors:
 #     - fan1
 #    target_interface: xyz.openbmc_project.Control.FanPwm
+#    target_path: /xyz/openbmc_project/control/fanpwm/