dt-bindings: mmc: convert bcm2835-sdhost bindings to YAML

Convert the DT binding document for bcm2835-sdhost from .txt to YAML.

Signed-off-by: Stefan Wahren <stefan.wahren@i2se.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20230604121223.9625-9-stefan.wahren@i2se.com


Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>