r8169: use spinlock to protect access to registers Config2 and Config5

[ Upstream commit 6bc6c4e6 ]

For disabling ASPM during NAPI poll we'll have to access both registers
in atomic context. Use a spinlock to protect access.

Reviewed-by: Simon Horman <simon.horman@corigine.com>
Tested-by: Kai-Heng Feng <kai.heng.feng@canonical.com>
Tested-by: Holger Hoffstätte <holger@applied-asynchrony.com>
Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Stable-dep-of: 5e864d90 ("r8169: skip DASH fw status checks when DASH is disabled")
Signed-off-by: Sasha Levin <sashal@kernel.org>