mt76: sdio: lock sdio when it is needed

Acquire the SDIO as needed as possible because either MT7663S or MT7921S
is a multiple-function device that always includes Bluetooth that would
share with the same SDIO bus. So not to avoid breaking Bluetooth pairing,
audio, and HID such kind of time critical application on that, we only
lock sdio bus when it is necessary in WiFi driver.

Signed-off-by: Sean Wang <sean.wang@mediatek.com>
Signed-off-by: Felix Fietkau <nbd@nbd.name>