HID: multitouch: enable palm rejection for Windows Precision Touchpad

The usage Confidence is mandary to Windows Precision Touchpad devices. If
it is examined in input_mapping on a WIndows Precision Touchpad, a new add
quirk MT_QUIRK_CONFIDENCE desgned for such devices will be applied to the
device. A touch with the confidence bit is not set is determined as
invalid.

Tested on Dell XPS13 9343

Cc: stable@vger.kernel.org # v4.5+
Reviewed-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>
Tested-by: Andy Lutomirski <luto@kernel.org> # XPS 13 9350, BIOS 1.4.3
Signed-off-by: Allen Hung <allen_hung@dell.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>