net: pcs: xpcs: use generic register definitions

As a general policy, we refer our generic register definitions over
vendor specific definitions. In XPCS, it appears that the register
layout follows a BMCR, BMSR and ADVERTISE register definition. We
already refer to this BMCR register using several different macros
which is confusing.

Convert the following register definitions to generic versions:

DW_VR_MII_MMD_CTRL => MII_BMCR
MDIO_CTRL1 => MII_BMCR
AN_CL37_EN => BMCR_ANENABLE
SGMII_SPEED_SS6 => BMCR_SPEED1000
SGMII_SPEED_SS13 => BMCR_SPEED100
MDIO_CTRL1_RESET => BMCR_RESET

DW_VR_MII_MMD_STS => MII_BMSR
DW_VR_MII_MMD_STS_LINK_STS => BMSR_LSTATUS

DW_FULL_DUPLEX => ADVERTISE_1000XFULL
iDW_HALF_DUPLEX => ADVERTISE_1000XHALF

Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Tested-by: Serge Semin <fancer.lancer@gmail.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>