Add touchscreen node as i2c1 slave device on Engicam Is.IoT MX6UL
modules, the touchscreen controlled 'st,stmpe-ts' connected via
i2c with st,stmpe811 mfd interface.

Cc: Matteo Lisi <matteo.lisi@engicam.com>
Cc: Michael Trimarchi <michael@amarulasolutions.com>
Signed-off-by: NJagan Teki <jagan@amarulasolutions.com>
Signed-off-by: NShawn Guo <shawnguo@kernel.org>