ARM: dts: vf500-colibri: Add device tree node for touchscreen support

Add device tree node for touchscreen support on Colibri VF50. The
touchscreen functionality on VF50 uses the ADC channels of Vybrid
and some GPIOs. Also add pinctrl nodes for proper pinmux.

Signed-off-by: Sanchayan Maity <maitysanchayan@gmail.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>