arm64: dts: qcom: sm8450: move SDHCI pin configuration to DTSI

The SDHCI pin configuration/mux nodes are actually common to all
upstreamed boards, so define them in SoC DTSI to reduce code
duplication.

Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>

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In theory drive strength belongs to the board DTS, not SoC DTSI, but I
am following the advice here:
https://lore.kernel.org/lkml/CAD=FV=VUL4GmjaibAMhKNdpEso_Hg_R=XeMaqah1LSj_9-Ce4Q@mail.gmail.com/