arm64: dts: renesas: r8a779g0: Add Cortex-A76 1.8 GHz opp

Add an operating point for running the Cortex-A76 CPU cores on R-Car
V4H at 1.8 GHz (High Performance mode).

Based on a patch in the BSP by Tho Vu.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://lore.kernel.org/r/cc2bae27776523f499d01655ef18fe463a3ae1ae.1670492384.git.geert+renesas@glider.be