fix(morello): dts: remove #a-c and #s-c from memory node

The #address-cells and #size-cells properties affect the size of reg
properties in *child* nodes only, they have no effect on the current
node.

The /memory node has no children, hence there is no need to specify
those properties. dt-validate complains about this:
==========
morello-soc.dtb: /: memory@80000000: '#address-cells', '#size-cells' do
                 not match any of the regexes: 'pinctrl-[0-9]+'
From schema: dt-schema.git/dtschema/schemas/memory.yaml
==========

Remove the unneeded properties.

Change-Id: I35058a00fa9bfa1007f31a4c21898dd45c586aa8
Signed-off-by: Andre Przywara <andre.przywara@arm.com>