ARM: dts: add Luckfox Pico Mini B USB host variant

[kkbin505]

ARM: dts: add Luckfox Pico Mini B USB host variant

The existing RV1103 Luckfox Pico Mini DTS selects USB peripheral mode. A Mini B used with an external USB Wi-Fi adapter needs a host configuration. Add a dedicated rv1103g-luckfox-pico-mini-b-usb-host.dts target that includes the existing Mini DTS, identifies the Mini B host variant, and overrides the DWC3 role to host. Register its DTB in the Rockchip build list.

The variant inherits Mini's SPI NAND and camera configuration and disabled Ethernet. Existing Mini peripheral and Pico Plus OTG defaults are unchanged. NAND image partitioning, boot arguments, WLAN package selection and WFB defaults remain device-profile work for OpenIPC/builder.

This replaces the approach of forcing Pico Plus into host mode in the downstream RV1103 firmware. Related firmware split: OpenIPC/firmware#2411.

Validation:

• Based on OpenIPC/linux rockchip-rv1106 commit 75a3a5b.
• Preprocessed and compiled the new variant, original Mini and original Plus DTS with GCC and the existing Buildroot host dtc; all three succeeded.
• Compared decoded new and Mini DTBs: only model and dr_mode differ.
• The new variant has the same existing DTC warning categories as the Mini baseline; no additional warning category was introduced.
• Hardware boot/video validation of this exact Mini B DTS is pending. Earlier successful Mini B RTL8812AU video tests used a patched Pico Plus target and are not evidence that this new target has passed.

Keep as draft until a builder profile selects the new target and the Mini B is tested. No USB hub compatibility claim is made.