net: dsa: sja1105: SGMII and 2500base-x on the SJA1110 are 'special'

For the xMII Mode Parameters Table to be properly configured for SGMII
mode on SJA1110, we need to set the "special" bit, since SGMII is
officially bitwise coded as 0b0011 in SJA1105 (decimal 3, equal to
XMII_MODE_SGMII), and as 0b1011 in SJA1110 (decimal 11).

Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>