ARM64: dts: meson-gx: make efuse read-only

efuse is one time programmable, so it is safer to deny write request
to this memory, unless the user is savvy enough to remove the read-only
flag from DTB

Signed-off-by: Jerome Brunet <jbrunet@baylibre.com>
Signed-off-by: Kevin Hilman <khilman@baylibre.com>