cpsw: support the HWTSTAMP ioctl and the CPTS

This patch hooks into the CPTS code and adds support for the HWTSTAMP
ioctl. The patch includes code for the CPSW version found in the dm814x
even though the background device tree support for this board is still
missing.

Signed-off-by: Richard Cochran <richardcochran@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>