net: phy: motorcomm: use device properties for firmware tuning

The Motorcomm PHY driver reads optional firmware properties via
of_property_read_*() from phydev->mdio.dev.of_node. This works for
Device Tree based systems, but causes ACPI platforms to ignore the same
properties when they are supplied through _DSD.

As a result, ACPI-described Motorcomm PHY devices fall back to default
settings instead of applying firmware-provided tuning such as
rx/tx internal delay, drive strength, clock output frequency, and
optional boolean controls like auto-sleep-disabled,
keep-pll-enabled, and tx clock inversion.

Switch these lookups to device_property_read_*() so the driver uses the
generic firmware node interface and can consume the same property names
from either Device Tree or ACPI.

This keeps the existing DT behavior unchanged while allowing ACPI
platforms to honor PHY configuration from firmware.

We have completed testing on Sophgo RISC-V architecture server SD3-10.
This server has a 64-core Thead C920 CPU whose DWMAC is connected to
Motorcomm's PHY YT8531. This server supports UEFI boot and it would like
to use the ACPI table.

Signed-off-by: chunzhi.lin <linchunzhi0@gmail.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Link: https://patch.msgid.link/20260507040221.3679454-2-linchunzhi0@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>