dt-bindings: mmc: controller: move properties common with slot out to mmc-controller-common

Move the common MMC "slot" properties because they are shared by the
single-slot or multi-slot controllers, and will help defining a simple
mmc-slot bindings document with proper slot properties and nodename.

Reviewed-by: Rob Herring (Arm) <robh@kernel.org>
Signed-off-by: Neil Armstrong <neil.armstrong@linaro.org>
Message-ID: <20241128-topic-amlogic-arm32-upstream-bindings-fixes-convert-meson-mx-sdio-v4-2-11d9f9200a59@linaro.org>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>