HID: magicmouse: Implement Multi-touch Protocol B (MT-B)

The driver for Apple Magic Trackpad/Mouse currently uses
Multi-touch Protocol A (MT-A) to report touch events and uses
ABS_MT_TRACKING_ID to do finger tracking. The fact of the device
being able to track individual finger makes it possible to
report touch events using MT-B. This patch converts the driver
to use MT-B as it is preferred to MT-A.

V4: Removed BTN_TOUCH evnet.
V3: Removed the single touch related logic.
V2: Converting entirely to MT-B as Henrik Rydberg suggested.

Signed-off-by: Yufeng Shen <miletus@chromium.org>
Reviewed-and-tested-by: Henrik Rydberg <rydberg@euromail.se>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>