platform/chrome: cros_ec: Call interrupt bottom half in ISH or RPMSG mode

Call the same bottom half for all EC protocols (threaded code).

Signed-off-by: Gwendal Grignou <gwendal@chromium.org>
Signed-off-by: Enric Balletbo i Serra <enric.balletbo@collabora.com>
Link: https://lore.kernel.org/r/20210122054637.1422289-2-gwendal@chromium.org