arm64: dts: imx: Fix imx8*-var-som touchscreen property sizes

The common touchscreen properties are all 32-bit, not 16-bit. These
properties must not be too important as they are all ignored in case of an
error reading them.

Signed-off-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/Yk3moe6Hz8ELM0iS@robh.at.kernel.org'
Signed-off-by: Arnd Bergmann <arnd@arndb.de>