HID: multitouch: simplify the settings of the various features

The Win8 spec also declare other features we want to support:
latency and surface and button switches.

Though it doesn't seem we need to activate those by default, we have been
proved in the past that manufacturers rely on the Windows driver behavior
so we better mimic it to prevent further issues.

The current way of setting the features is cumbersome. It avoids iterating
over the list of features, but the way we store/retrieve the data just
doesn't scale with more than two values.

So iterate over the features when we decide to switch on the device and
make it simpler to extend.

Signed-off-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>