wifi: rtw89: phy: set TX power according to RF path number by chip

Previously, all supported chips had two RF paths. Therefore, these
codes used static number for TX power setting. Now, we are planning
to support a new chip which has only one RF path. So, we refine the
setting codes to refer to chip's RF path number at runtime.

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/20230203065157.8227-1-pkshih@realtek.com