Before submitting a new scroll mode, click method or sendevents mode check if
the value is supported by the device. This avoids BadValue errors when setting
two-finger scrolling on single-finger touchpad devices since we can't easily
handle BadValue (see 9747277b)
https://bugzilla.gnome.org/show_bug.cgi?id=750816
Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>