HID: rmi: Make hid-rmi a transport driver for synaptics-rmi4

The Synaptics RMI4 driver provides support for RMI4 devices. Instead of
duplicating the RMI4 processing code, make hid-rmi a transport driver
and register it with the Synaptics RMI4 core.

Signed-off-by: Andrew Duggan <aduggan@synaptics.com>
Signed-off-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>