net: ethernet: mediatek: enhance the locking using the lightweight ones

Since these critical sections protected by page_lock are all entered
from the user context or bottom half context, they can be replaced
with the spin_lock() or spin_lock_bh instead of spin_lock_irqsave().

Signed-off-by: Sean Wang <sean.wang@mediatek.com>
Acked-by: John Crispin <john@phrozen.org>
Signed-off-by: David S. Miller <davem@davemloft.net>