platform/chrome: wilco_ec: Add version sysfs entries

Add the ability to extract version information from the EC.

Example Output:
$ cd /sys/bus/platform/devices/GOOG000C:00
$ tail build_date build_revision version model_number
==> build_date <==
04/25/19

==> build_revision <==
d2592cae0

==> version <==
00.00.14

==> model_number <==
08B6

Signed-off-by: Raul E Rangel <rrangel@chromium.org>
Reviewed-by: Nick Crews <ncrews@chromium.org>
Signed-off-by: Enric Balletbo i Serra <enric.balletbo@collabora.com>