net: phy: re-design phy_modes to be self-contained

of_get_phy_mode() uses a local array to map phy_interface_t values from
include/linux/net/phy.h to a string which is read from the 'phy-mode' or
'phy-connection-type' property. In preparation for exposing the PHY
interface mode through sysfs, perform the following:

- mode phy_modes from drivers/of/of_net.c to include/linux/phy.h such
  that it is right below the phy_interface_t enum
- make it a static inline function returning the string such that we can
  use it by just including include/linux/net/phy.h
- add a PHY_INTERFACE_MODE_MAX enum value to guard the iteration in
  of_get_phy_mode()

Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
net: phy: expose PHY device interface mode

Expose the PHY device interface mode through sysfs since this is an
useful piece of information for knowing how the attached networking
device will have configured its transmit/receive path.

Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
net: phy: add "has_fixups" boolean property

Add a boolean property which indicates if the PHY has had any fixup
routine ran on it. We are later going to use that boolean to expose it
as a sysfs property to help troubleshooting.

Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
net: phy: expose phydev->has_fixups to sysfs

Expose the PHY device has_fixups boolean as a sysfs property to help
troubleshooting PHY configurations.

Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>