This driver implements a slim layer to enable the ChromeOS
EC kernel stack (cros_ec) to communicate with ChromeOS EC
firmware running on the Intel Integrated Sensor Hub (ISH).
The driver registers a ChromeOS EC MFD device to connect
with cros_ec kernel stack (upper layer), and it registers a
client with the ISH Transport Protocol bus (lower layer) to
talk with the ISH firwmare. See description of the ISHTP
protocol at Documentation/hid/intel-ish-hid.txt