arm64: dts: r8a7795: Add CA53 L2 cache-controller node

Add a device node for the Cortex-A53 L2 cache-controller.

The L2 cache for the Cortex-A53 CPU cores is 512 KiB large (organized as
32 KiB x 16 ways).

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
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v3:
  - Remaining part of "[PATCH v2 6/6] arm64: renesas: r8a7795: Add L2
    cache-controller nodes".