ARM: dts: meson8: fix GPU interrupts and drop an undocumented property

The interrupts in Amlogic's vendor kernel sources are all contiguous.
There are two typos leading to pp2 and pp4 as well as ppmmu2 and ppmmu4
incorrectly sharing the same interrupt line.
Fix this by using interrupt 170 for pp2 and 171 for ppmmu2.

Also 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: 7d3f6b53

 ("ARM: dts: meson8: add the Mali-450 MP6 GPU")
Signed-off-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Signed-off-by: Kevin Hilman <khilman@baylibre.com>