dt-bindings: mmc: sdhci: document sdhci-caps and sdhci-caps-mask

The Linux SDHCI driver core reads 'sdhci-caps' and 'sdhci-caps-mask'
properties and few devices already use it (e.g. Qualcomm SM8450), so add
them to a shared SDHCI bindings.

Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Reviewed-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20221204094717.74016-1-krzysztof.kozlowski@linaro.org
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>