net: dsa: sja1105: remove hwts_tx_en from tagger data

This tagger property is in fact not used at all by the tagger, only by
the switch driver. Therefore it makes sense to be moved to
sja1105_private.

Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>