The EPHY control part of the EMAC syscon register has a bit called
CLK_SEL. On the datasheet it says that if it's 0 the EPHY clock is 25MHz
and if it's 1 the clock is 24MHz.

However, according to the datasheets, no Allwinner SoC with EPHY has any
extra xtal input pins for the EPHY, and the system xtal is 24MHz.

That means the EPHY is not possible to get a 25MHz xtal input, and thus
the frequency can only be 24MHz.

It doesn't matter on H3 as the default value of H3 is 24MHz, however on
V3s the default value is wrongly set to 25MHz, which prevented the EPHY
from working properly.

Force the EPHY clock frequency to 24MHz.
Signed-off-by: Icenowy Zheng <icenowy@aosc.io>
Signed-off-by: David S. Miller <davem@davemloft.net>