arm64: dts: renesas: r8a77950: Drop operating points above 1.5 GHz

The higher operating frequencies for the Cortex-A57 CPU cores, which
were first documented in the R-Car Gen3 Hardware User's Manual revision
0.54, apply to R-Car H3 ES2.0 (r8a77951).

Play it safe and restrict R-Car H3 ES1.x to 1.5 GHz, by removing the
"turbo-mode" entries from the operating points table inherited from
r8a77951.dtsi.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://lore.kernel.org/r/20210311110552.3124180-1-geert+renesas@glider.be