units: Add Watt units

As there are the temperature units, let's add the Watt macros definition.
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Reviewed-by: Lukasz Luba <lukasz.luba@arm.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

include/linux/units.h

@@ -4,6 +4,10 @@
 
 #include <linux/kernel.h>
 
+#define MILLIWATT_PER_WATT	1000L
+#define MICROWATT_PER_MILLIWATT	1000L
+#define MICROWATT_PER_WATT	1000000L
+
 #define ABSOLUTE_ZERO_MILLICELSIUS -273150
 
 static inline long milli_kelvin_to_millicelsius(long t)