dts: meson-g12-common-u-boot: do not disable canvas

We were disabling canvas, which causes meson vpu probe failure,
just stop and leave canvas alone.

Fixes: ce9fa7bf ("ARM: dts: meson-g12a: add U-Boot specific DT for graphics")
Link: https://lore.kernel.org/r/20241008-u-boot-topic-g12-do-not-disable-canvas-v1-1-b89659370012@linaro.org


Signed-off-by: Neil Armstrong <neil.armstrong@linaro.org>