Input: cros_ec_keyb - add of match table

To enable the cros_ec_keyb driver to be auto-loaded when build as
module add an of match table (and export it) to match the modalias
information passed on to userspace as the Cros EC MFD driver registers
the MFD subdevices with an of_compatibility string.

Signed-off-by: Sjoerd Simons <sjoerd.simons@collabora.co.uk>
Reviewed-by: Javier Martinez Canillas <javier.martinez@collabora.co.uk>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>