wifi: rtw89: phy: set TX power offset according to chip gen

We have a register to control TX power of each rate section to increase
or decrease an offset. But, Wi-Fi 6 chips and Wi-Fi 7 chips have different
address and format for this control register. We rename original setting
stuffs with a suffix `_ax` and implement setting flow for Wi-Fi 7 chips.
Then, we set TX power offset 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/20231003015446.14658-4-pkshih@realtek.com