msg2138 only supports 2 fingers presses, and needs different processing
since second finger press is encoded as a delta position wrt. first one
and the packet/touch_event structs are not the same as msg2638.

Add support for it by implementing distinct structs and irq handler.
Signed-off-by: Vincent Knecht <vincent.knecht@mailoo.org>
Link: https://lore.kernel.org/r/20221110171952.34207-4-vincent.knecht@mailoo.orgSigned-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>