net: pcs: xpcs: add 1000BASE-X AN interrupt support

Enable CL37 AN complete interrupt for DW XPCS. It requires to clear the
bit(0) [CL37_ANCMPLT_INTR] of VR_MII_AN_INTR_STS after AN completed.

And there is a quirk for Wangxun devices to enable CL37 AN in backplane
configurations because of the special hardware design.

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