wifi: rtw89: add mac_gen pointer to access mac port registers

Using mac_gen pointer to reuse the code with WiFi 7 chips, and define
MAC ports registers for WiFi 7 chips.

Signed-off-by: Ping-Ke Shih <pkshih@realtek.com>
Signed-off-by: Kalle Valo <kvalo@kernel.org>
Link: https://lore.kernel.org/r/20230911082049.33541-7-pkshih@realtek.com