ARM: dts: imx6q-apalis: Disable stmpe touchscreen

Unify its label with other toradex SoM dtbs.
This allows to enable it in an overlay per the current
system configuration.

Signed-off-by: Oleksandr Suvorov <oleksandr.suvorov@toradex.com>
Signed-off-by: Max Krummenacher <max.krummenacher@toradex.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>