wifi: rtw89: introduce rtw89_chan for channel stuffs

Introduce struct rtw89_chan ahead to encapsulate stuffs from struct
rtw89_channel_params. These stuffs have a clone in HAL and are used
throughout driver. After multiple channels support, it's expected that
each channel instance has a configuration of them. So, we refine them
with struct rtw89_chan by precise type first, and will re-arrange HAL
by struct rtw89_chan in the following as well.

(No logic has changed.)

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/20220809104952.61355-3-pkshih@realtek.com