net: phy: broadcom: Remove unused flags

We have a number of unused flags defined today and since we are scarce
on space and may need to introduce new flags in the future remove and
shift every existing flag down into a contiguous assignment.
PHY_BCM_FLAGS_MODE_1000BX was only used internally for the BCM54616S
PHY, so we allocate a driver private structure instead to store that
flag instead of canibalizing one from phydev->dev_flags for that
purpose.

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