wifi: mt76: connac: rework macros for unified command

Rework some macros for connac3 unified command.
This is a preliminary patch to add mt7996 chipset support.

Signed-off-by: Peter Chiu <chui-hao.chiu@mediatek.com>
Signed-off-by: Shayne Chen <shayne.chen@mediatek.com>
Signed-off-by: Felix Fietkau <nbd@nbd.name>