net: qcom/emac: add support for emulation systems

On emulation systems, the EMAC's internal PHY ("SGMII") is not present,
but is not needed for network functionality.  So just display a warning
message and ignore the SGMII.

Tested-by: Philip Elcan <pelcan@codeaurora.org>
Tested-by: Adam Wallis <awallis@codeaurora.org>
Signed-off-by: Timur Tabi <timur@codeaurora.org>
Signed-off-by: David S. Miller <davem@davemloft.net>