arm64: dts: renesas: r8a774c0: Remove bogus voltages from OPP table

According to the RZ/G Series, 2nd Generation Hardware User’s Manual
Rev. 1.11, the System CPU cores on RZ/G2E do not have their own power
supply, but use the common internal power supply (typical 1.03V).

Hence remove the "opp-microvolt" properties from the Operating
Performance Points table.  They are optional, and unused, when none of
the CPU nodes is tied to a regulator using the "cpu-supply" property.

Fixes: 231d8908 ("arm64: dts: renesas: r8a774c0: Add OPPs table for cpu devices")
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://lore.kernel.org/r/8348e18a011ded94e35919cd8e17c0be1f9acf2f.1676560856.git.geert+renesas@glider.be