net: dsa: qca8k: add support for pws config reg

Some qca8327 switch require to force the ignore of power on sel
strapping. Some switch require to set the led open drain mode in regs
instead of using strapping. While most of the device implements this
using the correct way using pin strapping, there are still some broken
device that require to be set using sw regs.
Introduce a new binding and support these special configuration.
As led open drain require to ignore pin strapping to work, the probe
fails with EINVAL error with incorrect configuration.

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