net: dsa: sja1105: add the RX timestamping procedure for SJA1110

This is really easy, since the full RX timestamp is in the DSA trailer
and the tagger code transfers it to SJA1105_SKB_CB(skb)->tstamp, we just
need to move it to the skb shared info region. This is as opposed to
SJA1105, where the RX timestamp was received in a meta frame (so there
needed to be a state machine to pair the 2 packets) and the timestamp
was partial (so the packet, once matched with its timestamp, needed to
be added to an RX timestamping queue where the PTP aux worker would
reconstruct that timestamp).

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