UPSTREAM: clk: rockchip: rk3036: rename emac ext source clock

UPSTREAM: clk: rockchip: rk3036: rename emac ext source clock

There is only support rmii in the RK3036, so we should use the correct
ext clock name as described in the TRM.

Change-Id: Idf1ba727690f364f7705f15a8dac1b570c773044
Signed-off-by: Xing Zheng <zhengxing@rock-chips.com>
[update dt-binding document as well]
Signed-off-by: Heiko Stuebner <heiko@sntech.de>
Signed-off-by: Caesar Wang <wxt@rock-chips.com>
(cherry picked from git.kernel.org next/linux-next.git master
 commit 01b4557d30e95c64cfdc96025e75207647524ec2)