net: phylink: add helper to initialize phylink's phydev

commit 6d6d6cce7eadec4f28df3776399cec143ead47c3 from
https://github.com/linux4microchip/linux.git

 linux-6.6-mchp+fpga

Add helper to initalize phydev embedded in a phylink object.

Signed-off-by: Claudiu Beznea <claudiu.beznea@microchip.com>
Signed-off-by: harish h <harish.h@windriver.com>