HID: wacom: Support switching from vendor-defined device mode on G9 and G11

A tablet PC booted into Windows may have its pen/touch hardware switched
into "Wacom mode" similar to what we do with explicitly-supported hardware.
Some devices appear to maintain this state across reboots, preventing their
use with the generic HID driver. This patch adds support for detecting the
presence of the mode switch feature report used by devices based on the G9
and G11 chips and has the HID codepath always attempt to reset the device
back to sending standard HID reports.

Fixes: https://sourceforge.net/p/linuxwacom/bugs/307/
Fixes: https://sourceforge.net/p/linuxwacom/bugs/310/
Fixes: https://github.com/linuxwacom/input-wacom/issues/15

Co-authored-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>
Signed-off-by: Jason Gerecke <jason.gerecke@wacom.com>
Reviewed-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>