mfd: cros_ec: Instantiate properly CrOS ISH MCU device

Integrated Sensor Hub (ISH) is also a MCU running EC
having feature bit EC_FEATURE_ISH. Instantiate it as
a special CrOS EC device with device name 'cros_ish'.

Signed-off-by: Rushikesh S Kadam <rushikesh.s.kadam@intel.com>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@intel.com>
Acked-by: Enric Balletbo i Serra <enric.balletbo@collabora.com>
Reviewed-by: Gwendal Grignou <gwendal@chromium.org>
Signed-off-by: Lee Jones <lee.jones@linaro.org>