dt-bindings: aspeed-sgpio: Convert txt bindings to yaml.

sgpio-aspeed bindings should be converted to yaml format.

Signed-off-by: Steven Lee <steven_lee@aspeedtech.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Link: https://lore.kernel.org/r/20210712100317.23298-2-steven_lee@aspeedtech.com


Signed-off-by: Joel Stanley <joel@jms.id.au>