dt-bindings: Drop unnecessary pinctrl properties

For a single pinctrl mode, it is not necessary to define pinctrl
properties as the tools always allow pinctrl properties.

Signed-off-by: Rob Herring <robh@kernel.org>
Acked-by: Charles Keepax <ckeepax@opensource.cirrus.com>
Acked-by: Mark Brown <broonie@kernel.org>
Acked-by: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>
Link: https://lore.kernel.org/r/20220119015325.2438277-1-robh@kernel.org