Add the missing L2 cache-controller node, and link the CPU node to it.
This will allow migration to the generic l2c OF initialization.

The L2 cache is an ARM L2C-310 (r3p1-150rel0), of size 256 KiB (32 KiB x
8 ways).
Signed-off-by: NGeert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: NSimon Horman <horms+renesas@verge.net.au>