arm64: dts: r8a7795: Add missing properties to CA57 L2 cache node

Add the missing "cache-unified" and "cache-level" properties to the
Cortex-A57 cache-controller node.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Acked-by: Dirk Behme <dirk.behme@de.bosch.com>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>