wifi: rt2x00: add r calibration for MT7620

Add r calibration code as found in mtk driver.

Signed-off-by: Tomislav Požega <pozega.tomislav@gmail.com>
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/e0c34f233089bec4eb73826bc4f512166ee25934.1663445157.git.daniel@makrotopia.org