ARM: dts: dra7: Move cpus node to parent dts for dra74x and dra72x

Nearly all of the information in the cpus node, especially for cpu0, is
the same between dra74x and dra72x so move the common information to
the parent dra7.dtsi to avoid duplication of data.

Signed-off-by: Dave Gerlach <d-gerlach@ti.com>
Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Tony Lindgren <tony@atomide.com>