ARM: dts: imx6q-bx50v3: configure unused pca953x pins

At power on, pca953x GPIO pins are configured as input and may cause
unexpected interrupts. Configure the unused pins as GPO low to
avoid unexpected interrupts.

Signed-off-by: Ken Lin <ken.lin@advantech.com.tw>
Signed-off-by: Akshay Bhat <akshay.bhat@timesys.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>