In zynqmp platforms where firmware supports dynamic SGMII configuration
but has other non-SGMII ethernet devices, it fails them with no packets
received at the RX interface.
To fix this behaviour perform SGMII dynamic configuration only
for the SGMII phy interface.
Fixes: 32cee7818111 ("net: macb: Add zynqmp SGMII dynamic configuration support")
Signed-off-by: Radhey Shyam Pandey <radhey.shyam.pandey@xxxxxxx>