HID: magicmouse: disable and add module param for scroll acceleration

Scroll acceleration is unique to the magicmouse driver, and is
unintuitive to a user who is unaware of the functionality. Thus, disable
it by default, but add a module parameter to enable it for power users
who want it.

Signed-off-by: Chase Douglas <chase.douglas@canonical.com>
Acked-by: Michael Poole <mdpoole@troilus.org>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>