cros_ec: Drop old EC version support from EC driver

There is no need to support old style EC moving forward. Ultimately we
should get rid of the check_version() API. For now just return error
in case the EC does not seem to support the new API.

Reviewed-by: Vadim Bendebury <vbendeb@google.com>
Tested-by: Vadim Bendebury <vbendeb@google.com>
Signed-off-by: Vadim Bendebury <vbendeb@chromium.org>
Signed-off-by: Simon Glass <sjg@chromium.org>