Input: elantech/SMBus - export all capabilities from the PS/2 node

The recent touchpads might not have all the information regarding the
characteristics through the I2C port.
On some Lenovo t480s, this results in the touchpad not being detected
as a clickpad, and on the Lenovo P52, this results in a failure while
fetching the resolution through I2C.

We need to imitate the Windows behavior: fetch the data under PS/2, and
limit the querries under I2C.

This patch prepares this by exporting the info from PS/2.

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