ptp_qoriq: support automatic configuration for ptp timer

This patch is to support automatic configuration for ptp timer.
If required ptp dts properties are not provided, driver could
try to calculate a set of default configurations to initialize
the ptp timer. This makes the driver work for many boards which
don't have the required ptp dts properties in current kernel.
Also the users could set dts properties by themselves according
to their requirement.

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