net: phy: bcm7xxx: Fix 7425 PHY ID and flags

While adding support for 7425 PHY in the 7xxx PHY driver, the ID that
was used was actually coming from an external PHY: a BCM5461x. Fix this
by using the proper ID for the internal 7425 PHY and set the
PHY_IS_INTERNAL flag, otherwise consumers of this PHY driver would not
be able to properly identify it as such.

Fixes: d068b02c

 ("net: phy: add BCM7425 and BCM7429 PHYs")
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Reviewed-by: Petri Gynther <pgynther@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>