wifi: ath12k: Prepare ahvif scan link for parallel scan

When two split-phy devices that support overlapping frequency ranges within
the same band(say 5 GHz low and 5 GHz high) 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).

When a scan is triggered with frequency list containing frequencies of
both 5 GHz low and 5 GHz high, mac80211 generates a single scan request
to driver with all the frequencies. This is because mac80211 splits the
scan request based on band.

ath12k checks the first frequency in the requested scan frequency list and
initiates scan to corresponding radio's(ar) firmware with all the
frequencies. Firmware rejects this scan since some of the frequencies in
the scan request are not supported, resulting in a scan failure.
To fix this ath12k driver should split the scan request into multiple
scans based on requested frequencies and schedule them to corresponding
underlying radio(s) in parallel.

Currently, ath12k driver assigns the scan link (link 15) in ahvif->links[]
for scan vdev creation. However, with parallel scan support being
introduced in the following patch, multiple radios (e.g., 5 GHz low and
5 GHz high) in the same HW group may attempt to use the same scan link
concurrently, causing conflicts where the vdev created by one radio could
be deleted and re-initialized by another.

To address this, reserve space for additional scan links for each radio in
a MLO group and allow subsequent radios to use different available scan
links (ahvif->link[15..MAX_SCAN_LINKS]) when scan link (15) is
pre-occupied.
While at it, rename ATH12K_DEFAULT_SCAN_LINK as ATH12K_FIRST_SCAN_LINK
as there is no longer only one scan link.

Tested-on: QCN9274 hw2.0 PCI WLAN.WBE.1.4.1-00199-QCAHKSWPL_SILICONZ-1

Signed-off-by: Rameshkumar Sundaram <rameshkumar.sundaram@oss.qualcomm.com>
Reviewed-by: Mahendran P <quic_mahep@quicinc.com>
Link: https://patch.msgid.link/20250507194832.2501668-2-rameshkumar.sundaram@oss.qualcomm.com
Signed-off-by: Jeff Johnson <jeff.johnson@oss.qualcomm.com>

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