rtw88: 8822c: Add gap-k calibration to improve long range performance

gap-k is a calibration mechanism to eliminate power gaps between
two nearly rate groups.

This mechanism improves performance in long range test by applying
proper power value to those rate groups which have nonlinear power gap.

Signed-off-by: Guo-Feng Fan <vincent_fann@realtek.com>
Signed-off-by: Ping-Ke Shih <pkshih@realtek.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/20210419003748.3224-3-pkshih@realtek.com