The appletouch driver has grown up from supporting only a couple of
touchpads into supporting many touchpads, which can have different
number of sensors, different aspect ratios etc.

This patch cleans up the current driver code and makes it easy to
support the features of each different touchpad.

As a side effect, this patch also modifies the 'Y' multiplication factor
of the 'geyser3' and 'geyser4' touchpads (found on Core Duo and Core2
Duo MacBook and MacBook Pro laptops) in order to make the touchpad
output match the aspect ratio of the touchpad (Y factor changed from 43
to 64).

[dtor@mail.ru: make atp_info constant]
Signed-off-by: Stelian Pop <stelian@popies.net>
Acked-by: Johannes Berg <johannes@sipsolutions.net>
Signed-off-by: Dmitry Torokhov <dtor@mail.ru>