wifi: rtw89: phy: support ch_info per PHY

The ch_info is to record current channel info such as minimum RSSI of
connected stations, and to assist in dynamic mechanisms of DIG and EDCCA.

Move the struct to PHY context, so the dynamic mechanisms can use the info
of the same PHY.

Signed-off-by: Ping-Ke Shih <pkshih@realtek.com>
Link: https://patch.msgid.link/20250117072828.16728-6-pkshih@realtek.com