cros_ec: Add MEC LPC protocol variant

MEC accesses certain I/O regions through its EMI interface rather than
through LPC directly.

BUG=chrome-os-partner:38224
TEST=Manual on Glower. Verify system boots kernel cleanly in recovery
mode.
BRANCH=None

Change-Id: I405917999efb1d5760266acd4819e5f30f8167f7
Signed-off-by: Shawn Nematbakhsh <shawnn@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/263814
Reviewed-by: Duncan Laurie <dlaurie@chromium.org>
3 files changed