wifi: rtw89: phy: refine helpers used for raw TX power

Originally, these helpers were implemented by macros. We rewrite them
by normal functions. In the new function to seek raw TX power by rate,
we access the array according to rate section and discard the original
pointer arithmetic.

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/20230920074322.42898-5-pkshih@realtek.com