ARM: sun4i: Add muxing options for the ethernet controller

The EMAC only has one pinset available for muxing, so hopefully, we
cover all cases.

Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>
Tested-by: Richard Genoud <richard.genoud@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>