dt-bindings: i2c: nomadik: support 400kHz < clock-frequency <= 3.4MHz

Hardware is not limited to 400kHz, its documentation does mention how to
configure it for high-speed (a specific Speed-Mode enum value and
a different bus rate clock divider register to be used).

Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Théo Lebrun <theo.lebrun@bootlin.com>
Reviewed-by: Rob Herring (Arm) <robh@kernel.org>
Signed-off-by: Andi Shyti <andi.shyti@kernel.org>
Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>