arm64: dts: ti: k3-am6xx-phycore-som: Add overlay to disable eth phy

arm64: dts: ti: k3-am6xx-phycore-som: Add overlay to disable eth phy

Add an overlay to disable the eth phy for all am6xx-phycore-som
boards.
The EEPROM on am6xx-phycore-soms contains information about the
configuration of the SOM. The standard configuration of the SOM
has an ethernet phy, but if no ethernet phy is populated, the EEPROM
will indicate that change and we can use this overlay to cleanly
disable the ethernet phy.

Signed-off-by: Nathan Morrisson <nmorrisson@phytec.com>
Link: https://lore.kernel.org/r/20240613230759.1984966-3-nmorrisson@phytec.com
Signed-off-by: Vignesh Raghavendra <vigneshr@ti.com>