Adding OpenWrt support for Xiaomi AX6000

I bring up a ipq5000+qcn6122 wifi6 router. based on qsdk 12.1 .
the kernel version I use is 5.15
ethernet and wifi is ok now.
the code is based on

manifest AU_LINUX_QSDK_NHSS.QSDK.12.1.R3_TARGET_ALL.12.1.03.841.039.xml
but the code is not based on openwrt. but I can send the kernel and driver patch to one interesting.