dt: bindings: net: use boolean dt properties for eee broken modes

The patches regarding eee-broken-modes was merged before all people
involved could find an agreement on the best way to move forward.

While we agreed on having a DT property to mark particular modes as broken,
the value used for eee-broken-modes mapped the phy register in very direct
way. Because of this, the concern is that it could be used to implement
configuration policies instead of describing a broken HW.

In the end, having a boolean property for each mode seems to be preferred
over one bit field value mapping the register (too) directly.

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