OpenWrt support for Xiaomi AX9000

@kirdes Finally got around to booting gain.
Here is the error:

[   11.156676] ath11k_pci 0000:01:00.0: chip_id 0x0 chip_family 0x0 board_id 0xff soc_id 0xffffffff
[   11.156715] ath11k_pci 0000:01:00.0: fw_version 0x2506844c fw_build_timestamp 2021-07-13 10:24 fw_build_id 
[   11.587059] ath11k_pci 0000:01:00.0: No regulatory rules available in the event info
[   11.587093] ath11k_pci 0000:01:00.0: failed to extract regulatory info from received event
[   11.593968] ------------[ cut here ]------------
[   11.601948] WARNING: CPU: 0 PID: 1975 at ath11k_hal_rx_reo_ent_buf_paddr_get+0x3238/0x431c [ath11k]
[   11.606714] Modules linked in: pppoe ppp_async iptable_nat ath11k_pci ath11k_ahb ath11k ath10k_pci ath10k_core ath xt_state xt_nat xt_conntrack xt_REDIRECT xt_MASQUERADE xt_FLOWOFFLOAD pppox ppp_generic nf_nat nf_flow_table nf_conntrack mac80211 ipt_REJECT cfg80211 xt_time xt_tcpudp xt_multiport xt_mark xt_mac xtg
[   11.656785] CPU: 0 PID: 1975 Comm: dropbearkey Tainted: G        W         5.10.72 #0
[   11.679021] Hardware name: Xiaomi AX9000 (DT)
[   11.686915] pstate: 60400005 (nZCv daif +PAN -UAO -TCO BTYPE=--)
[   11.691261] pc : ath11k_hal_rx_reo_ent_buf_paddr_get+0x3238/0x431c [ath11k]
[   11.697338] lr : ath11k_hal_rx_reo_ent_buf_paddr_get+0x3238/0x431c [ath11k]
[   11.704019] sp : ffffffc01138bbe0
[   11.710957] x29: ffffffc01138bc10 x28: ffffffc008c37f24 
[   11.714433] x27: ffffff8004cd4740 x26: ffffffc008aecec4 
[   11.719816] x25: 0000000000000000 x24: ffffff8006d80000 
[   11.725111] x23: ffffff8006d81d78 x22: 000000000003a001 
[   11.730406] x21: ffffff800559a880 x20: ffffff8006d80000 
[   11.735700] x19: ffffff8004c75100 x18: 0000000000000165 
[   11.740996] x17: 0000000000000000 x16: 0000000000000000 
[   11.746291] x15: ffffffc011277cc8 x14: 000000000000042f 
[   11.751585] x13: 0000000000000165 x12: ffffffc01138b7d8 
[   11.756881] x11: ffffffc0112cfcc8 x10: 00000000fffff000 
[   11.762175] x9 : ffffffc0112cfcc8 x8 : 0000000000000000 
[   11.767471] x7 : ffffffc011277cc8 x6 : 0000000000000001 
[   11.772766] x5 : 0000000000000000 x4 : 0000000000000000 
[   11.778061] x3 : 0000000000000000 x2 : 0000000000000000 
[   11.783357] x1 : ffffff8005bf5c00 x0 : 000000000000004e 
[   11.788652] Call trace:
[   11.793947]  ath11k_hal_rx_reo_ent_buf_paddr_get+0x3238/0x431c [ath11k]
[   11.796124]  ath11k_htc_rx_completion_handler+0x4c8/0x690 [ath11k]
[   11.802720]  ath11k_ce_per_engine_service+0x304/0x424 [ath11k]
[   11.808966]  ath11k_mhi_resume+0x5a4/0xc94 [ath11k_pci]
[   11.814785]  tasklet_action_common.constprop.0+0x15c/0x194
[   11.819903]  tasklet_action+0x2c/0x3c
[   11.825455]  _stext+0x124/0x290
[   11.829186]  irq_exit+0x70/0xa0
[   11.832140]  __handle_domain_irq+0x84/0xe0
[   11.835266]  gic_handle_irq+0x7c/0xa4
[   11.839431]  el0_irq_naked+0x4c/0x54
[   11.843162] ---[ end trace 033bd3e52faeb04c ]---
[   11.848101] ath11k_pci 0000:01:00.0: failed to receive default regd during init

No idea how the hell does a BDF do this