net: netcp: Consolidates statistics collection code

Different Keystone2 platforms have different number and
layouts of hw statistics modules.  This patch consolidates
the statistics processing of different Keystone2 platforms
for easy maintenance.

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