net: phy: broadcom: Allow enabling or disabling of EEE

In preparation for adding support for Wirespeed/downshift, we need to
change bcm_phy_eee_enable() to allow enabling or disabling EEE, so make
the function take an extra enable/disable boolean parameter and rename
it to illustrate it sets EEE, not necessarily just enables it.

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