ARM: dts: r8a73a4: Add L2 cache-controller nodes

Add device nodes for the L2 caches, and link the CPU node to its L2
cache node.

The L2 cache for the Cortex-A15 CPU cores is 1 MiB large (organized as
64 KiB x 16 ways), and located in PM domain A3SM.

The L2 cache for the Cortex-A7 CPU cores is 512 KiB large (organized as
64 KiB x 8 ways), and located in PM domain A3KM.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>