Input: synaptics-rmi4 - store the attn data in the driver

Now that we have a proper API to set the attention data, there is
no point in keeping it in the transport driver.

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