wifi: cfg80211: Add utility API to get radio index from channel

wifi: cfg80211: Add utility API to get radio index from channel

Add utility API cfg80211_get_radio_idx_by_chan() to retrieve the radio
index corresponding to a given channel in a multi-radio wiphy.

This utility function can be used when we want to check the radio-specific
data for a channel in a multi-radio wiphy. For example, it can help
determine the radio index required to handle a scan request. This index
can then be used to decide whether the scan can proceed without
interfering with ongoing DFS operations on another radio.

Signed-off-by: Vasanthakumar Thiagarajan <vasanthakumar.thiagarajan@oss.qualcomm.com>
Co-developed-by: Raj Kumar Bhagat <quic_rajkbhag@quicinc.com>
Signed-off-by: Raj Kumar Bhagat <quic_rajkbhag@quicinc.com>
Link: https://patch.msgid.link/20250527-mlo-dfs-acs-v2-1-92c2f37c81d9@quicinc.com
Signed-off-by: Johannes Berg <johannes.berg@intel.com>