dts: rk3308: Enable ethernet function supported for Firefly ROC_RK3308_CC

The Firefly ROC_RK3308_CC use ref_clock of input mode,
and rmii pins of m1 group.

Signed-off-by: David Wu <david.wu@rock-chips.com>
Reviewed-by: Kever Yang <kever.yang@rock-chips.com>