net: netcp: Fixes to CPSW statistics collection

In certain applications it's beneficial to allow the CPSW h/w
stats counters to continue to increment even while the kernel
polls them. This patch implements this behavior for both 1G
and 10G ethernet subsystem modules.

Signed-off-by: WingMan Kwok <w-kwok2@ti.com>
Signed-off-by: David S. Miller <davem@davemloft.net>