ARM: dts: meson8b: drop undocumented property from the Mali GPU node

Drop the undocumented "switch-delay" which is a left-over from my
experiments with an early lima kernel driver when it was still
out-of-tree and required this property on Amlogic SoCs.

Fixes: c3ea80b6 ("ARM: dts: meson8b: add the Mali-450 MP2 GPU")
Signed-off-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Signed-off-by: Kevin Hilman <khilman@baylibre.com>