Add power file owners

BUG=None
TEST=Compile.

Change-Id: I7db4fee7308aa5b90b5456bb68a2a7aee05497c5
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1737067Reviewed-by: Ryo Hashimoto <hashimoto@chromium.org>
Commit-Queue: Abhishek Bhardwaj <abhishekbh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#684226}

chromeos/dbus/power/OWNERS

+abhishekbh@chromium.org
+ejcaruso@chromium.org
+ravisadineni@chromium.org