net: phy: bcm7xxx: add BCM7250 and BCM7364 PHY entries

Add two new entries to the Broadcom BCM7xxx internal PHY driver for
BCM7250 and BCM7364 chips. Those chips share the usual 28nm process
Gigabit PHY sequence and require the same workarounds so far.

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