net: bcmgenet: reset 40nm EPHY on energy detect

The EPHY integrated into the 40nm Set-Top Box devices can falsely
detect energy when connected to a disabled peer interface. When the
peer interface is enabled the EPHY will detect and report the link
as active, but on occasion may get into a state where it is not
able to exchange data with the connected GENET MAC. This issue has
not been observed when the link parameters are auto-negotiated;
however, it has been observed with a manually configured link.

It has been empirically determined that issuing a soft reset to the
EPHY when energy is detected prevents it from getting into this bad
state.

Fixes: 1c1008c7 ("net: bcmgenet: add main driver file")
Signed-off-by: Doug Berger <opendmb@gmail.com>
Acked-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>