net: phy: realtek: eliminate priv->phycr1 variable

net: phy: realtek: eliminate priv->phycr1 variable

Previous changes have replaced the machine-level priv->phycr2 with a
high-level priv->disable_clk_out. This created a discrepancy with
priv->phycr1 which is resolved here, for uniformity.

One advantage of this new implementation is that we don't read
priv->phycr1 in rtl821x_probe() if we're never going to modify it.

We never test the positive return code from phy_modify_mmd_changed(), so
we could just as well use phy_modify_mmd().

I took the ALDPS feature description from commit d90db36a9e74 ("net:
phy: realtek: add dt property to enable ALDPS mode") and transformed it
into a function comment - the feature is sufficiently non-obvious to
deserve that.

Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Link: https://patch.msgid.link/20251117234033.345679-6-vladimir.oltean@nxp.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>