net: bcmgenet: Add 'eee' module parameter

On some switches, having EEE enabled causes the link to become
unstable. With this patch, adding 'genet.eee=N' to the kernel command
line will cause EEE to be disabled on the link.

See: https://github.com/raspberrypi/linux/issues/4289



Signed-off-by: Phil Elwell <phil@raspberrypi.com>