dpaa2-eth: define a global ptp_qoriq structure pointer

Define a global ptp_qoriq structure pointer, and export to use.
The ptp clock operations will be used in dpaa2-eth driver.
For example, supporting one step timestamping needs to write
current time to hardware frame annotation before sending and
then hardware inserts the delay time on frame during sending.
So in driver, at least clock gettime operation will be needed
to make sure right time is written to hardware frame annotation
for one step timestamping.

Signed-off-by: Yangbo Lu <yangbo.lu@nxp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>