coresight: remove gpio entries from dt documentation

Remove references for CoreSight TPIU gpio components from device
tree documentation since the TPIU driver now exclusively uses
pinctrl framewrok to support TPIU mictor trace instead of gpiolib.

Change-Id: I07fb7988b715e6f65a6c3fefc3eb088789384df9
Signed-off-by: Aparna Das <adas@codeaurora.org>