net: phy: workaround for buggy cable detection by LAN8700 after cable plugging

net: phy: workaround for buggy cable detection by LAN8700 after cable plugging

* Due to HW bug, LAN8700 sometimes does not detect presence of energy in the
  Ethernet cable in Energy Detect Power-Down mode (e.g while EDPWRDOWN bit is
  set, the ENERGYON bit does not asserted sometimes). This is a common bug of
  LAN87xx family of PHY chips.
* The lan87xx_read_status() was improved to acquire ENERGYON bit. Its previous
  algorythm still not reliable on 100 % and sometimes skip cable plugging.

Signed-off-by: Igor Plyatov <plyatov@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>