phy: bcm63xx: report Broadcom BCM63xx PHYs as internal

The Broadcom BCM63xx PHY driver is for the SoC internal PHYs, flag these
as internal PHY devices.

Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>