arm64: dts: freescale: imx8m*-venice-*: fix gw,gsc dt-schema warnings

Fix the dt-schema warnings due to #address-cells/#size-cells being
unnecessary when there are no children with reg cells.

Signed-off-by: Tim Harvey <tharvey@gateworks.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>