net: phy: Allow EEE for all RGMII variants

RGMII interfaces come in multiple flavors: RGMII with transmit or
receive internal delay, no delays at all, or delays in both direction.

This change extends the initial check for PHY_INTERFACE_MODE_RGMII to
cover all of these variants since EEE should be allowed for any of these
modes, since it is a property of the RGMII, hence Gigabit PHY capability
more than the RGMII electrical interface and its delays.

Fixes: a59a4d19 ("phy: add the EEE support and the way to access to the MMD registers")
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>