HID: multitouch: Add support for button type usage
According to [1], Windows Precision Touchpad devices must supply
a button type usage in the device capabilities feature report. A
value of 0 indicates that the device contains a depressible
button (i.e. it's a click-pad) whereas a value of 1 indicates
a non-depressible button. Add support for this usage and set
INPUT_PROP_BUTTONPAD on the touchpad input device whenever a
depressible button is present.