phylib: Add Vitesse VSC8221 SGMII PHY

PHY is mostly compatible with the existing VSC8244 PHY.  The init sequence
is different and the interrupt mask lacks some bits present in the VSC8244.

Rather than making a copy of the existing VSC234x config_intr function and
change one constant, I modify it to select the interrupt mask based on
which driver is calling it.  This lets it be used by both drivers.

Signed-off-by: Trent Piepho <tpiepho@freescale.com>
Signed-off-by: David S. Miller <davem@davemloft.net>