wifi: rt2x00: add RXDCOC calibration for MT7620

Add RXDCOC calibration code from mtk driver.

Signed-off-by: Tomislav Požega <pozega.tomislav@gmail.com>
[fixed typo reported by Serge Vasilugin <vasilugin@yandex.ru>]
Signed-off-by: Daniel Golle <daniel@makrotopia.org>
Acked-by: Stanislaw Gruszka <stf_xl@wp.pl>
Signed-off-by: Kalle Valo <kvalo@kernel.org>
Link: https://lore.kernel.org/r/850b30f652e88de30d79e968af4eb47aa5bc2511.1663445157.git.daniel@makrotopia.org