DWC2 USB mode blocks in rpi-config lack mutual exclusivity

[JianpengChang]

In recipes-bsp/bootfiles/rpi-config_git.bb, the three DWC2 USB mode configuration blocks (lines 250-267) have inconsistent exclusion logic,
which can result in multiple conflicting dtoverlay=dwc2,dr_mode=... lines being written to config.txt.

Current behavior:

• ENABLE_DWC2_PERIPHERAL excludes ENABLE_DWC2_OTG ✓
• ENABLE_DWC2_OTG excludes ENABLE_DWC2_PERIPHERAL ✓
• ENABLE_DWC2_HOST has no exclusion checks ✗

If a user sets both ENABLE_DWC2_HOST=1 and ENABLE_DWC2_PERIPHERAL=1 (or ENABLE_DWC2_OTG=1), both blocks fire and produce conflicting dtoverlay lines:

dtoverlay=dwc2,dr_mode=peripheral
dtoverlay=dwc2,dr_mode=host

According to the linux doc Documentation/devicetree/bindings/usb/usb-drd.yaml. It's an enum, only one dr_mode can be active, so the result is undefined.

Suggested fix:

Replace the three independent if blocks with an elif chain to make mutual exclusivity explicit:

if [ "${ENABLE_DWC2_OTG}" = "1" ]; then
    echo "# Enable USB OTG mode" >> $CONFIG
    echo "dtoverlay=dwc2,dr_mode=otg" >> $CONFIG
elif [ "${ENABLE_DWC2_PERIPHERAL}" = "1" ]; then
    echo "# Enable USB peripheral mode" >> $CONFIG
    echo "dtoverlay=dwc2,dr_mode=peripheral" >> $CONFIG
elif [ "${ENABLE_DWC2_HOST}" = "1" ]; then
    echo "# Enable USB host mode" >> $CONFIG
    echo "dtoverlay=dwc2,dr_mode=host" >> $CONFIG
fi