arm64: dts: renesas: r8a779g0: Add CPU core clocks

Describe the clocks for the four Cortex-A76 CPU cores.
CA76 Sub-Systems 0/1 (both clusters / all CPU cores) are clocked by Z0φ.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://lore.kernel.org/r/aa6e9ae21e451ebd40d54d986bd0296571128d5b.1668429870.git.geert+renesas@glider.be