dt-bindings: pinctrl: ralink: rt305x: split binding

The RT3352 and RT5350 SoCs each contain different pin muxing information,
therefore, should be split. This can be done now that there are compatible
strings to distinguish them from other SoCs.

Split the schema out to ralink,rt3352-pinctrl.yaml and
ralink,rt5350-pinctrl.yaml.

Remove ralink,rt3352-pinctrl and ralink,rt5350-pinctrl from rt305x.

Signed-off-by: Arınç ÜNAL <arinc.unal@arinc9.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20230317213011.13656-20-arinc.unal@arinc9.com
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>