HID: input: Create a utility class for counting scroll events

To avoid code duplication, this class counts high-resolution scroll
movements and emits the legacy low-resolution events when appropriate.
Drivers should be able to create one instance for each scroll wheel that
they need to handle.

Signed-off-by: Harry Cutts <hcutts@chromium.org>
Reviewed-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>