arm64: dts: Add support for Juno r2 board

Juno r2 is identical to Juno r1 with Cortex A57 cores replaced by
Cortex A72 cores.

Acked-by: Rob Herring <robh@kernel.org>
Acked-by: Liviu Dudau <Liviu.Dudau@arm.com>
Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>