Convert the Spreadtrum SC2731 regulator bindings to DT schema.

Change during conversion:
  - switch compatible from sprd,sc27xx-regulator to sprd,sc2731-regulator,
    same as the only in-tree user has done back in 2019 [1]

[1] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/arch/arm64/boot/dts/sprd/sc2731.dtsi?h=v6.9&id=0419a75b1808dda225b17ba1509f195f23c0db88Signed-off-by: Stanislav Jakubek <stano.jakubek@gmail.com>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Link: https://patch.msgid.link/ZobxoobZvA8k3pyi@standask-GA-A55M-S2HPSigned-off-by: Mark Brown <broonie@kernel.org>