cros_ec: Split cros_ec_devs module

This patch splits the cros_ec_devs module in two parts with a
cros_ec_dev module responsible for handling MFD devices registration and
a cros_ec_ctl module responsible for handling the various user-space
interfaces.

For consistency purpose, the driver name for the cros_ec_dev module is
now cros-ec-dev instead of cros-ec-ctl.

In the next commit, the new cros_ec_dev module will be moved to the MFD
subtree so mfd_add_devices() calls are not done from outside MFD.

Signed-off-by: Thierry Escande <thierry.escande@collabora.com>
Reviewed-by: Gwendal Grignou <gwendal@chromium.org>
Tested-by: Guenter Roeck <groeck@chromium.org>
Signed-off-by: Lee Jones <lee.jones@linaro.org>