net: phy: Add c45_phy_ids sysfs directory entry

net: phy: Add c45_phy_ids sysfs directory entry

The phy_id field only shows the PHY ID of the C22 device, and the C45
device did not store its PHY ID in this field.

Add a new phy_mmd_group, and export the mmd<n>_device_id for the C45
device. These files are invisible to the C22 device.

Signed-off-by: Yajun Deng <yajun.deng@linux.dev>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Link: https://patch.msgid.link/20250613131903.2961-1-yajun.deng@linux.dev
Signed-off-by: Paolo Abeni <pabeni@redhat.com>