arm64: dts: renesas: Rename numbered regulators

Numbered regulators are prone to conflicts, causing silent overwrites
(see e.g. [1]).

Make conflicts less likely to happen by renaming all numbered regulators
to names reflecting the regulator's purposes.

[1] commit 45f5d5a9 ("arm64: dts: renesas: r8a77995: draak: Fix
    backlight regulator name").

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://lore.kernel.org/r/b90dfeb834c4d7dabd22bf03396f33df58f54507.1652264651.git.geert+renesas@glider.be