net: dsa: qca8k: add support for qca8327 switch

qca8327 switch is a low tier version of the more recent qca8337.
It does share the same regs used by the qca8k driver and can be
supported with minimal change.

Signed-off-by: Ansuel Smith <ansuelsmth@gmail.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Reviewed-by: Vladimir Oltean <olteanv@gmail.com>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>