net: phy: dp83867: Extend RX strap quirk for SGMII mode

When RX strap in HW is not set to MODE 3 or 4, bit 7 and 8 in CF4
register should be set. The former is already handled in
dp83867_config_init; add the latter in SGMII specific initialization.

Fixes: 2a10154a

 ("net: phy: dp83867: Add TI dp83867 phy")
Signed-off-by: Harini Katakam <harini.katakam@amd.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>