Input: synaptics - warn the users when there is a better mode

The Synaptics touchpads are now either using i2c-hid or rmi-smbus.
Warn the users if they are missing the rmi-smbus modules and have no
chance of reporting correct data.

Signed-off-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>