net: phy: consolidate PHY reset in phy_init_hw()

There are quite a lot of drivers touching a PHY device MII_BMCR
register to reset the PHY without taking care of:

1) ensuring that BMCR_RESET is cleared after a given timeout
2) the PHY state machine resuming to the proper state and re-applying
potentially changed settings such as auto-negotiation

Introduce phy_poll_reset() which will take care of polling the MII_BMCR
for the BMCR_RESET bit to be cleared after a given timeout or return a
timeout error code.

In order to make sure the PHY is in a correct state, phy_init_hw() first
issues a software reset through MII_BMCR and then applies any fixups.

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

Documentation/networking/phy.txt

@@ -255,7 +255,8 @@ Writing a PHY driver
 
    config_init: configures PHY into a sane state after a reset.
      For instance, a Davicom PHY requires descrambling disabled.
-   probe: Does any setup needed by the driver
+   probe: Allocate phy->priv, optionally refuse to bind.
+   PHY may not have been reset or had fixups run yet.
    suspend/resume: power management
    config_aneg: Changes the speed/duplex/negotiation settings
    read_status: Reads the current speed/duplex/negotiation settings