HID: multitouch: report MT_TOOL_PALM for non-confident touches

HID: multitouch: report MT_TOOL_PALM for non-confident touches

According to Microsoft specification [1] for Precision Touchpads (and
Touchscreens) the devices use "confidence" reports to signal accidental
touches, or contacts that are "too large to be a finger". Instead of
simply marking contact inactive in this case (which causes issues if
contact was originally proper and we lost confidence in it later, as
this results in accidental clicks, drags, etc), let's report such
contacts as MT_TOOL_PALM and let userspace decide what to do.

[1] https://docs.microsoft.com/en-us/windows-hardware/design/component-guidelines/touchpad-windows-precision-touchpad-collection

Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>
[splitted and rebased]
Signed-off-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>