net: ethernet: ti: am65-cpsw: Add suspend/resume support

Add PM handlers for System suspend/resume.

As DMA driver doesn't yet support suspend/resume we free up
the DMA channels at suspend and acquire and initialize them
at resume.

Move the init/free dma calls to ndo_open/close() hooks so
it is symmetric and easier to invoke from suspend/resume handler.

As CPTS looses contect during suspend/resume, invoke the
necessary CPTS suspend/resume helpers.

Signed-off-by: Roger Quadros <rogerq@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>