arm64: dts: sdm845: Add CPU topology

The 8 CPU cores of the SDM845 are organized in two clusters of 4 big
("gold") and 4 little ("silver") cores. Add a cpu-map node to the DT
that describes this topology.

Signed-off-by: Matthias Kaehlcke <mka@chromium.org>
Reviewed-by: Douglas Anderson <dianders@chromium.org>
Signed-off-by: Andy Gross <agross@kernel.org>