net: dsa: microchip: lan937x: add support for configuing xMII register

This patch add the common ksz_set_xmii function for ksz series switch
and update the lan937x code phylink mac config. The register address for
the ksz8795 is Port 5 Interface control 6 and for all other switch is
xMII Control 1.
The bit value for selecting the interface is same for
KSZ8795 and KSZ9893 are same. The bit values for KSZ9477 and lan973x are
same. So, this patch add the bit value for each switches in
ksz_chip_data and configure the registers based on the chip id.

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