power: Add power to cros_ec-access

Add the power user to the cros_ec-access group.

BUG=chromium:1036363
TEST=Confirm that the power user is added to the cros_ec-access group.

Cq-Depend: chromium:1988765
Change-Id: Iff1d244bdec62cc09ac1731fc2bb30b847ca504a
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/overlays/eclass-overlay/+/1993543
Tested-by: Kartik Hegde <khegde@chromium.org>
Commit-Queue: Kartik Hegde <khegde@chromium.org>
Reviewed-by: Jorge Lucangeli Obes <jorgelo@chromium.org>