ARM: dts: msm8916: add release pinctrl node for TS

Add pingroups for touchscreen GPIOs that allows
releasing pinctrl mux ownership. These nodes don't
have a pin-function property associated with them
and is explicitly used by each touch driver to
release the mux ownership of each GPIO pin during
error paths in driver.

Change-Id: Ibd70680f57409749ce91bc2867c17e3b15486325
Signed-off-by: Shantanu Jain <shjain@codeaurora.org>