Instead of sticking it in rockchip.c

I've already done this on Armbian Legacy kernel, leaving the drivers unchanged, leaving the I2C entries out of rockchip.c.
added to rk3288-miniarm.dts:

&i2c3 {
status = "okay";

tinker_ft5406:tinker_ft5406@38 {
    compatible = "tinker_ft5406";
    reg = <0x38>;
};

tinker_mcu:tinker_mcu@45 {
    compatible = "tinker_mcu";
    reg = <0x45>;
};

};

Also, the tinker_mcu and asus_mcu are redundant but different (unless there is some special hardware floating around?) I'm using the tinker_mcu driver successfully, omitted the asus_mcu files entirely. Just thought one less bit of Tinker-specific kernel code to keep track of might be nice.