rtw88: 8821c: add cck pd settings

CCK PD can reduce the number of false alarm of the CCK rates.
It dynamically adjusts the power threshold and CS ratio.
The values are compared to the values of the previous level, if
the level is changed, set new values of power threshold and CS
ratio.

Implement rtw_chip_ops::cck_pd_set() for 8821c.

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/20200603094218.19942-2-yhchuang@realtek.com