rtw88: 8821c: add set channel support

8821c is capable of 2.4G and 5G.

Implement rtw_chip_ops::set_channel() to set 2G and 5G channels.
This includes MAC, BB and RF related settings.

Reviewed-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Tzu-En Huang <tehuang@realtek.com>
Signed-off-by: Yan-Hsuan Chuang <yhchuang@realtek.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/20200616091625.26489-5-yhchuang@realtek.com