[Bug 297618] GPIO pinctrl overlays fail silently on rk3566 for UARTs on M1+

https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=297618

            Bug ID: 297618
           Summary: GPIO pinctrl overlays fail silently on rk3566 for
                    UARTs on M1+
           Product: Base System
           Version: 15.1-RELEASE
          Hardware: arm64
                OS: Any
            Status: New
          Severity: Affects Many People
          Priority: ---
         Component: arm
          Assignee: [email protected]
          Reporter: [email protected]

On FreeBSD 15.1-RELEASE and FreeBSD 16.0-CURRENT, pins on GPIO headers do not
respond on a Radxa Zero 3E / RK3566 when enabled with overlays if they are a
multiplexing variant 1 or higher.

UART3_RX_M0, UART3_TX_M0: works
UART4_RX_M1, UART4_RX_M1: fails


### References

I'm using a Radxa Zero 3E. Anything but M0 seem to fail:
https://docs.radxa.com/en/zero/zero3/hardware-design/hardware-interface

Other users experiencing problems. Patches discussed:
https://forums.freebsd.org/threads/enabling-uarts-on-rk3566-radxa-zero-3e.101491/


### Exact steps to reproduce

cat << EOF >> /root/uart3.dtso
/dts-v1/;
/plugin/;

/ {
    compatible = "radxa,zero3", "rockchip,rk3566";

    fragment@0 {
        target = <&uart3>;
        __overlay__ {
            status = "okay";
            pinctrl-names = "default";
            pinctrl-0 = <&uart3m0_xfer>;
        };
    };
};
EOF


cat << EOF >> /root/uart4.dtso
/dts-v1/;
/plugin/;

/ {
    compatible = "radxa,zero3", "rockchip,rk3566";

    fragment@0 {
        target = <&uart4>;
        __overlay__ {
            status = "okay";
            pinctrl-names = "default";
            pinctrl-0 = <&uart4m1_xfer>;
        };
    };
};
EOF

dtc -O dtb -o /boot/dtb/overlays/rk3566-uart3-enable.dtbo -b 0 -@
/root/uart3.dtso
dtc -O dtb -o /boot/dtb/overlays/rk3566-uart4-enable.dtbo -b 0 -@
/root/uart4.dtso

vi /boot/loader.conf
```
# Overlays
fdt_overlays="rk3566-uart3-enable.dtbo,rk3566-uart4-enable.dtbo"
```

reboot

# Loopback Test S3 and S4
pkg install picocom

picocom -b 115200 --flow none --databits 8 --parity none --stopbits 1
/dev/cuau1
# result: works (characters echo)

picocom -b 115200 --flow none --databits 8 --parity none --stopbits 1
/dev/cuau2
# result: fails (no output on screen)

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