CrOS EC: Consolidate "hello" test

The "hello" test is commonly used to test if communication works and
that the EC supports the protocol version we're using. This patch
places the test in the generic gec.c file and updates call sites.

BUG=none
BRANCH=none
TEST=Tested on Link (LPC), Snow (I2C), and Kirby (SPI)

Change-Id: I9541d6862dae06eb2f03af34eeb3cace6881cec5
Reviewed-on: https://chromium-review.googlesource.com/175636
Reviewed-by: Yung-chieh Lo <yjlou@chromium.org>
Commit-Queue: David Hendricks <dhendrix@chromium.org>
Tested-by: David Hendricks <dhendrix@chromium.org>
5 files changed