net: dsa: microchip: add the phylink get_caps

This patch add the support for phylink_get_caps for ksz8795 and ksz9477
series switch. It updates the struct ksz_switch_chip with the details of
the internal phys and xmii interface. Then during the get_caps based on
the bits set in the structure, corresponding phy mode is set.

Signed-off-by: Arun Ramadoss <arun.ramadoss@microchip.com>
Reviewed-by: Vladimir Oltean <olteanv@gmail.com>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>