net: dsa: microchip: ksz9477: use common xmii function

In ksz9477.c file, configuring the xmii register is performed based on
the flag NEW_XMII. The flag is reset for ksz9893 switch and set for
other switch. This patch uses the ksz common xmii set and get function.
The bit values are configured based on the chip id.

Signed-off-by: Arun Ramadoss <arun.ramadoss@microchip.com>
Signed-off-by: David S. Miller <davem@davemloft.net>