net: pcs: xpcs: adapt Wangxun NICs for SGMII mode

net: pcs: xpcs: adapt Wangxun NICs for SGMII mode

Wangxun NICs support the connection with SFP to RJ45 module. In this case,
PCS need to be configured in SGMII mode.

According to chapter 6.11.1 "SGMII Auto-Negitiation" of DesignWare Cores
Ethernet PCS (version 3.20a) and custom design manual, do the following
configuration when the interface mode is SGMII.

1. program VR_MII_AN_CTRL bit(3) [TX_CONFIG] = 1b (PHY side SGMII)
2. program VR_MII_AN_CTRL bit(8) [MII_CTRL] = 1b (8-bit MII)
3. program VR_MII_DIG_CTRL1 bit(0) [PHY_MODE_CTRL] = 1b

Also CL37 AN in backplane configurations need to be enabled because of the
special hardware design. Another thing to note is that PMA needs to be
reconfigured before each CL37 AN configuration for SGMII, otherwise AN will
fail, although we don't know why.

On this device, CL37_ANSGM_STS (bit[4:1] of VR_MII_AN_INTR_STS) indicates
the status received from remote link during the auto-negotiation, and
self-clear after the auto-negotiation is complete.
Meanwhile, CL37_ANCMPLT_INTR will be set to 1, to indicate CL37 AN is
complete. So add another way to get the state for CL37 SGMII.

Signed-off-by: Jiawen Wu <jiawenwu@trustnetic.com>
Signed-off-by: David S. Miller <davem@davemloft.net>