cros_ec: Honor the google,remote-bus dt property

Boards where ECs that use a I2C port != 0 specify this in the
devicetree file via the google,remote-bus property.
Previously this was ignored and hardcoded to port 0.

Signed-off-by: Moritz Fischer <moritz.fischer@ettus.com>
Cc: Simon Glass <sjg@chromium.org>
Cc: Heiko Schocher <hs@denx.de>
Cc: u-boot@lists.denx.de
Acked-by: Simon Glass <sjg@chromium.org>