cros: add cros_ec driver

This patch adds the cros_ec driver that implements the protocol for
communicating with Google's ChromeOS embedded controller.

Signed-off-by: Bernie Thompson <bhthompson@chromium.org>
Signed-off-by: Bill Richardson <wfrichar@chromium.org>
Signed-off-by: Che-Liang Chiou <clchiou@chromium.org>
Signed-off-by: Doug Anderson <dianders@chromium.org>
Signed-off-by: Gabe Black <gabeblack@chromium.org>
Signed-off-by: Hung-ying Tyan <tyanh@chromium.org>
Signed-off-by: Louis Yung-Chieh Lo <yjlou@chromium.org>
Signed-off-by: Randall Spangler <rspangler@chromium.org>
Signed-off-by: Sean Paul <seanpaul@chromium.org>
Signed-off-by: Simon Glass <sjg@chromium.org>
Signed-off-by: Vincent Palatin <vpalatin@chromium.org>
Acked-by: Simon Glass <sjg@chromium.org>
Tested-by: Simon Glass <sjg@chromium.org>