rtw89: 8852c: implement chip_ops::get_thermal

Read thermal value, and then we can use EWMA thermal value to do RF
calibrations if the value is changed over a threshold.

Signed-off-by: Ping-Ke Shih <pkshih@realtek.com>
Signed-off-by: Kalle Valo <kvalo@kernel.org>
Link: https://lore.kernel.org/r/20220421120903.73715-13-pkshih@realtek.com