wifi: rtw89: add chip_info::chip_gen to determine chip generation

The coming WiFi 7 chip is 8922AE which uses different hardware rate and
register naming rule. Adding a chip_info::chip_gen field can help to
do things by generations accordingly.

Signed-off-by: Ping-Ke Shih <pkshih@realtek.com>
Signed-off-by: Kalle Valo <kvalo@kernel.org>
Link: https://lore.kernel.org/r/20230728070252.66525-2-pkshih@realtek.com