wifi: mt76: mt76x02: fix MT76x0 external LNA gain handling

On MT76x0, LNA gain should be applied for both external and internal LNA.
On MT76x2, LNA gain should be treated as 0 for external LNA.
Move the LNA type based logic to mt76x2 in order to fix mt76x0.

Fixes: 2daa6758

 ("mt76x0: unify lna_gain parsing")
Reported-by: Shiji Yang <yangshiji66@outlook.com>
Signed-off-by: Felix Fietkau <nbd@nbd.name>
Signed-off-by: Kalle Valo <kvalo@kernel.org>
Link: https://lore.kernel.org/r/20230919194747.31647-1-nbd@nbd.name