units: Add Watt units

[ Upstream commit 2ee5f8f0

 ]

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>
Stable-dep-of: c8c37bc5

 ("i2c: designware: use casting of u64 in clock multiplication to avoid overflow")
Signed-off-by: Sasha Levin <sashal@kernel.org>