wifi: ath12k: combine channel list for split-phy devices in single-wiphy

wifi: ath12k: combine channel list for split-phy devices in single-wiphy

When two split-phy devices that support overlapping frequency ranges within
the same band are grouped into an ath12k hardware (HW) setup, they share a
common wiphy instance. Consequently, the channel list (wiphy->bands[])
becomes unified across all associated radios (ar).

For reference, the devices are:
2.4 GHz + 5 GHz Low Band
5 GHz High Band + 6 GHz

The first radio probed within the 5 GHz range (say 5 GHz Low Band) updates
its sband reference (&ar->mac.sbands[NL80211_BAND_5GHZ]) within
wiphy->bands[]. However, when the second 5 GHz radio (5 GHz High Band) is
probed, it replaces the existing wiphy->bands[] entry with its own sub-band
reference. As a result, wiphy->bands[] always reflects the channel list
from the most recently probed radio in that band, restricting supported
channels to those within its specific range for upper-layer.

Fix this by updating the wiphy->bands[] to just enable the channels of
current radio when there exist a radio which already has set it.
This will make sure wiphy->bands[] holds reference of first radio which
got probed in 5 GHz band and subsequent radio just updates the channel list
in the same address space.

Since same sband memory space is shared between radios of a band, while
determining the allowed frequency range of radio, its frequency limits
(ar->freq_range.start_freq, end_freq) should be used.

Tested-on: QCN9274 hw2.0 PCI WLAN.WBE.1.4.1-00199-QCAHKSWPL_SILICONZ-1
Tested-on: WCN7850 hw2.0 PCI WLAN.HMT.1.1.c5-00284-QCAHMTSWPL_V1.0_V2.0_SILICONZ-1

Signed-off-by: Rameshkumar Sundaram <rameshkumar.sundaram@oss.qualcomm.com>
Reviewed-by: Vasanthakumar Thiagarajan <vasanthakumar.thiagarajan@oss.qualcomm.com>
Link: https://patch.msgid.link/20250522111514.3735107-1-rameshkumar.sundaram@oss.qualcomm.com
Signed-off-by: Jeff Johnson <jeff.johnson@oss.qualcomm.com>