input: synaptics_i2c_rmi4: add support for pinctrl framework

Migrate the Synaptics driver to use pinctrl framework for GPIO
configuration so that driver is compatible with targets that
use and targets that don't use pinctrl framework.

Change-Id: Ib20fe5a01a1a06c783c69f9da5d1c8379597c542
Signed-off-by: Himanshu Aggarwal <haggarwa@codeaurora.org>
Signed-off-by: Guoping Yu <guopingy@codeaurora.org>