net: mvpp2: debugfs: Allow reading the C2 engine table from debugfs

PPv2's Classifier uses multiple engines to perform classification. So
far, only the C2 engine is used, which has a 256 entries TCAM.

So far, we only accessed the relevant entries from the C2 engines, which
are the one implementing RSS. To implement and debug ntuple
classification offload, beaing able to see the hit count for each C2
entry is helpful, so this commit moves the logic to a dedicated
directory allowing to access each entry.

Signed-off-by: Maxime Chevallier <maxime.chevallier@bootlin.com>
Signed-off-by: David S. Miller <davem@davemloft.net>