arm64: dts: meson-gx: add back dmc register range until canvas driver is available
The Linux VPU bindings have changed and dropped the dmc register range.
Add it back in the meson-gx-u-boot.dtsi file until a proper canvas driver
is available.
Fixes: dd5f2351e9 ("arm64: dts: meson: sync dt and bindings from v5.6-rc2")
Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>