wifi: rtw89: phy: set TX power RU limit according to chip gen

Wi-Fi 6 chips and Wi-Fi 7 chips have different register design for TX
power RU limit. We rename original setting stuffs with a suffix `_ax`,
concentrate related enum declaration in phy.h, and implement setting
flow for Wi-Fi 7 chips. Then, we set TX power RU limit according to
chip generation.

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/20231003015446.14658-6-pkshih@realtek.com