mt76: mt7615: use v1 MCU API on MT7615 to fix issues with adding/removing stations

The implementation of embedding WTBL update inside the STA_REC update is buggy
on the MT7615 v2 firmware. This leads to connection issues after a station has
connected and disconnected again.

Switch to the v1 MCU API ops, since they have received much more testing and
should be more stable.

On MT7622 and later, the v2 API is more actively used, so we should keep using
it as well.

Fixes: 6849e29e ("mt76: mt7615: add starec operating flow for firmware v2")
Cc: stable@vger.kernel.org
Signed-off-by: Felix Fietkau <nbd@nbd.name>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/20200812102332.11812-1-nbd@nbd.name