net: phy: split locked and unlocked section of phy_state_machine()

Split out the locked and unlocked sections of phy_state_machine() into
two separate functions which can be called inside the phydev lock and
outside the phydev lock as appropriate, thus allowing us to combine
the locked regions in the caller of phy_state_machine() with the
locked region inside phy_state_machine().

This avoids unnecessarily dropping the phydev lock which may allow
races to occur.

Tested-by: Jijie Shao <shaojijie@huawei.com>
Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Reviewed-by: Florian Fainelli <florian.fainelli@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>