wifi: cfg80211: Add debugfs support for multi-radio wiphy

wifi: cfg80211: Add debugfs support for multi-radio wiphy

In multi-radio wiphy architecture, where a single wiphy can have
multiple radios tied to it, radio specific configuration parameters
and global wiphy parameters are maintained for the entire physical
device and common to all radios. But, each radio in a wiphy can have
different values for each radio configuration parameter, like RTS
threshold. With the current debugfs directory structure, the values
of global wiphy configuration parameters can be viewed, but, values
of individual radio configuration parameters cannot be viewed, as
radio specific configuration parameters are not maintained, separately.

To address this, in addition to maintaining global wiphy configuration
parameters common to all radios, create separate debugfs directories
for each radio in a wiphy to maintain parameters corresponding to that
radio in this directory.

In implementation, maintain a dentry structure in wiphy_radio_cfg, a
structure  containing radio configurations of a wiphy. This struct is
maintained to denote per-radio configurations of a wiphy. Create
separate directories representing each radio within phy#X directory in
debugfs during wiphy registration.

Sample directory structure with this change:
ls /sys/kernel/debug/ieee80211/phy0/radio
radio0/ radio1/ radio2/

Signed-off-by: Roopni Devanathan <quic_rdevanat@quicinc.com>
Link: https://patch.msgid.link/20251024044649.483557-2-quic_rdevanat@quicinc.com
Signed-off-by: Johannes Berg <johannes.berg@intel.com>