HID: apple: Add support for the 2013 Macbook Air

This patch adds keyboard support for MacbookAir6,2 as WELLSPRING8
(0x0291, 0x0292, 0x0293). The touchpad is handled in a separate
bcm5974 patch, as usual.

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: Jiri Kosina <jkosina@suse.cz>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>