Input: bcm5974 - add support for the 2013 MacBook Air

The June 2013 Macbook Air (13'') has a new trackpad protocol; four new
values are inserted in the header, and the mode switch is no longer
needed. This patch adds support for the new devices.

Cc: stable@vger.kernel.org
Reported-and-tested-by: Brad Ford <plymouthffl@gmail.com>
Signed-off-by: Henrik Rydberg <rydberg@euromail.se>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>