wifi: mac80211: don't use cfg80211_chandef_create() for default chandef

wifi: mac80211: don't use cfg80211_chandef_create() for default chandef

cfg80211_chandef_create() is called universally to create the
default chandef during hw registration, however it only really
makes sense to be used for 2GHz, 5GHz, and 6GHz (and by extension
the 'LC' band) as it relies on the channel type which is only
relevant to those specific bands.

To reduce some confusion, create a generic helper for creating the
default chandef that makes sense for all supported bands.

Suggested-by: Johannes Berg <johannes@sipsolutions.net>
Signed-off-by: Lachlan Hodges <lachlan.hodges@morsemicro.com>
Link: https://patch.msgid.link/20260312045804.362974-2-lachlan.hodges@morsemicro.com
Signed-off-by: Johannes Berg <johannes.berg@intel.com>