HID: multitouch: enable palm rejection if device implements confidence usage

The usage Confidence is mandary to Windows Precision Touchpad devices. The
appearance of this usage is checked in hidinput_connect but the quirk
MT_QUIRK_VALID_IS_CONFIDENCE is not applied to device accordingly.
Apply this quirk and also remove quirk MT_QUIRK_ALWAYS_VALID to enable palm
rejection for the WIN 8 touchpad devices which have implemented usage
Confidence in its input reports.

Tested on Dell XPS 13 laptop.

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