wifi: rtw89: create rtw89_chan centrally to avoid breakage

Sometimes we need to write current rtw89_chan outside set_channel(),
e.g. during HW scan, we adjust it to align FW process through C2H.
However, we don't have full parameters to fill entire rtw89_chan.
And it will breakage if we update only part of current rtw89_chan.
That is what we don't want to see because most flows throughout
driver treat rtw89_chan as a whole.

So, we divide struct rtw89_chan to basic part and derived part. The
basic part contains the parameters which we are always able to know.
And the derived part will be calculated by the basic part. Then, a
central function, rtw89_chan_create(), is added to deal with this.

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/20220809104952.61355-5-pkshih@realtek.com