mt76: mt7921: make all event parser reusable between mt7921s and mt7921e

The longer event such as the event for mcu_get_nic_capability would hold
the data in paged fragment skb for the SDIO device so we turn the skb to
be linearized skb before accessing it to reuse the same event parser
betweem mt7921s and mt7921e.

Tested-by: Deren Wu <deren.wu@mediatek.com>
Acked-by: Lorenzo Bianconi <lorenzo@kernel.org>
Signed-off-by: Sean Wang <sean.wang@mediatek.com>
Signed-off-by: Felix Fietkau <nbd@nbd.name>