arm64: dts: morello: Fix-up cache nodes

There's no need include the CPU number in the L2 cache node names as
the names are local to the CPU nodes. The documented node name is
also just "l2-cache".

The L3 cache is not part of cpu@0/l2-cache as it is shared among all
cores. Move it to /cpus node which is the typical place for shared
caches.

Signed-off-by: Rob Herring (Arm) <robh@kernel.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Message-Id: <20250403-dt-cpu-schema-v1-3-076be7171a85@kernel.org>
Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>