net: stmmac: check if MAC needs to attach to a PHY

After the introduction of the fixed-link support, the MAC driver
no longer attempt to scan for a PHY to attach to. This causes the
non fixed-link setups to stop working.

Using the phylink_expects_phy() to check and determine if the MAC
should expect and attach a PHY.

Fixes: ab21cf92

 ("net: stmmac: make mdio register skips PHY scanning for fixed-link")
Signed-off-by: Michael Sit Wei Hong <michael.wei.hong.sit@intel.com>
Signed-off-by: Lai Peter Jun Ann <peter.jun.ann.lai@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>