wifi: mt76: connac: add data field in struct tlv

Add tlv->data element for tlv parsing easier.

This is a preliminary patch to support mt7925 driver.

Co-developed-by: Lorenzo Bianconi <lorenzo@kernel.org>
Signed-off-by: Lorenzo Bianconi <lorenzo@kernel.org>
Signed-off-by: Deren Wu <deren.wu@mediatek.com>
Signed-off-by: Felix Fietkau <nbd@nbd.name>