net: dsa: microchip: Support optional 125MHz SYNCLKO output

The KSZ9477 series chips have a SYNCLKO pin which by default outputs a
25MHz clock, but some board setups require a 125MHz clock instead. Added
a microchip,synclko-125 device tree property to allow indicating a
125MHz clock output is required.

Signed-off-by: Robert Hancock <hancock@sedsystems.ca>
Signed-off-by: David S. Miller <davem@davemloft.net>