net: phy: meson-gxl: Add generic dummy stubs for MMD register access

stable inclusion
from stable-v5.10.168
commit 98c93a01608f23a28a3c9e6736f74d078fa8400f
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I7URR4

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=98c93a01608f23a28a3c9e6736f74d078fa8400f



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[ Upstream commit afc2336f ]

The Meson G12A Internal PHY does not support standard IEEE MMD extended
register access, therefore add generic dummy stubs to fail the read and
write MMD calls. This is necessary to prevent the core PHY code from
erroneously believing that EEE is supported by this PHY even though this
PHY does not support EEE, as MMD register access returns all FFFFs.

Fixes: 5c3407ab ("net: phy: meson-gxl: add g12a support")
Reviewed-by: Heiner Kallweit <hkallweit1@gmail.com>
Signed-off-by: Chris Healy <healych@amazon.com>
Reviewed-by: Jerome Brunet <jbrunet@baylibre.com>
Link: https://lore.kernel.org/r/20230130231402.471493-1-cphealy@gmail.com


Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: zhaoxiaoqiang11 <zhaoxiaoqiang11@jd.com>