net: dsa: add KSZ9893 switch tagging support

KSZ9893 switch is similar to KSZ9477 switch except the ingress tail tag
has 1 byte instead of 2 bytes.  The size of the portmap is smaller and
so the override and lookup bits are also moved.

Signed-off-by: Tristram Ha <Tristram.Ha@microchip.com>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>