Input: bcm5974 - add driver for Macbook Air and Pro Penryn touchpads

This driver adds support for the multitouch trackpad on the new
Apple Macbook Air and Macbook Pro Penryn laptops. It replaces the
appletouch driver on those computers, and integrates well with the
synaptics driver of the Xorg system.

[dtor@mail.ru: various cleanups]
Signed-off-by: Henrik Rydberg <rydberg@euromail.se>
Signed-off-by: Dmitry Torokhov <dtor@mail.ru>