arm64: dts: renesas: r8a779m8: Drop operating points above 1.5 GHz

The highest-performance mode for the Cortex-A57 CPU cores supported on
R-Car H3Ne (R8A779M8) is the Power Optimized (1.5 GHz) mode.  The Normal
(1.6 GHz) and High Performance (1.7 GHz) modes are not supported.

Hence drop the "turbo-mode" entries from the operating points table
inherited from r8a77951.dtsi.

Fixes: 6e87525d ("arm64: dts: renesas: Add Renesas R8A779M8 SoC support")
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://lore.kernel.org/r/aeb4530f7fbac8329b334dcb169382c836a5f32d.1655458564.git.geert+renesas@glider.be