cpsw: simplify the setup of the register pointers

Instead of having a host of different register offsets in the device tree,
this patch simplifies the CPSW code by letting the driver set the proper
register offsets automatically, based on the CPSW version.

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