net: dsa: qca8k: move driver to qca dir

Move qca8k driver to qca dir in preparation for code split and
introduction of ipq4019 switch based on qca8k.

Signed-off-by: Christian Marangi <ansuelsmth@gmail.com>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>