Documentation: fpga: dfl: add descriptions for thermal/power management interfaces

This patch add introductions to thermal/power interfaces. They are
implemented as hwmon sysfs interfaces by thermal/power private
feature drivers.
Signed-off-by: Xu Yilun <yilun.xu@intel.com>
Signed-off-by: Wu Hao <hao.wu@intel.com>
Acked-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Moritz Fischer <mdf@kernel.org>

Documentation/fpga/dfl.rst

@@ -108,6 +108,16 @@ More functions are exposed through sysfs
      error reporting sysfs interfaces allow user to read errors detected by the
      hardware, and clear the logged errors.
 
+ Power management (dfl_fme_power hwmon)
+     power management hwmon sysfs interfaces allow user to read power management
+     information (power consumption, thresholds, threshold status, limits, etc.)
+     and configure power thresholds for different throttling levels.
+
+ Thermal management (dfl_fme_thermal hwmon)
+     thermal management hwmon sysfs interfaces allow user to read thermal
+     management information (current temperature, thresholds, threshold status,
+     etc.).
+
 
 FIU - PORT
 ==========