input: synaptics: make pinctrl support optional

Amend Synaptics touch driver to optionally take a pinctrl
handle and set the state of pins during boot. Some platforms
do not support pinctrl and making pinctrl support an optional
feature of the driver, allows this driver to be used on
those platforms as well.

Change-Id: I3c6c39c56161da9b6fa10302865d6ff8728683e9
Signed-off-by: Himanshu Aggarwal <haggarwa@codeaurora.org>