ath9k: experimental support for QCN5502

Based on openwrt 23.05.1. See openwrt#9389. .config used to build:

CONFIG_TARGET_ath79=y
CONFIG_TARGET_ath79_generic=y
CONFIG_TARGET_MULTI_PROFILE=y
CONFIG_TARGET_DEVICE_ath79_generic_DEVICE_asus_rt-ac59u=y
CONFIG_TARGET_DEVICE_ath79_generic_DEVICE_asus_rt-ac59u-v2=y
CONFIG_TARGET_DEVICE_ath79_generic_DEVICE_asus_zenwifi-cd6n=y
CONFIG_TARGET_DEVICE_ath79_generic_DEVICE_asus_zenwifi-cd6r=y
CONFIG_TARGET_DEVICE_ath79_generic_DEVICE_netgear_ex7300-v2=y
CONFIG_TARGET_DEVICE_ath79_generic_DEVICE_tplink_archer-a9-v6=y
CONFIG_TARGET_PER_DEVICE_ROOTFS=y
CONFIG_PACKAGE_luci=y