ARM: dts: imx6ul: mba6ulx: Fix stmpe811 node warnings

interrupt-controller is only valid for gpio subnode, remove it.
Rename touchscreen subnode according to bindings.

Signed-off-by: Alexander Stein <alexander.stein@ew.tq-group.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>