arm64: dts: renesas: r8a779a0: Add CPU0 core clock

Describe the clock for the first Cortex-A76 CPU core.
For now no operating points are defined.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://lore.kernel.org/r/3ace4eea4ff1cdc0f7b8ea7d0433c1063d795785.1654701400.git.geert+renesas@glider.be