wifi: rtw89: mac: do bf_monitor only if WiFi 6 chips

Beamforming monitor is used to adjust registers to fine tune performance
and power save, and currently only existing WiFi 6 chips need it.

Signed-off-by: Zong-Zhe Yang <kevin_yang@realtek.com>
Signed-off-by: Ping-Ke Shih <pkshih@realtek.com>
Signed-off-by: Kalle Valo <kvalo@kernel.org>
Link: https://lore.kernel.org/r/20231012021455.19816-7-pkshih@realtek.com