Documentation: EM: Switch to micro-Watts scale

The EM now uses the micro-Watts scale for the power values. Update
related documentation to reflect that fact.

Fix also a problematic sentence in the doc "to:" which triggers test
scripts complaining about wrong email address.

Reviewed-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Signed-off-by: Lukasz Luba <lukasz.luba@arm.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>