net: mvpp2: debugfs: add entries for classifier flows

The classifier configuration for RSS is quite complex, with several
lookup tables being used. This commit adds useful info in debugfs to
see how the different tables are configured :

Added 2 new entries in the per-port directory :

  - .../eth0/default_rxq : The default rx queue on that port
  - .../eth0/rss_enable : Indicates if RSS is enabled in the C2 entry

Added the 'flows' directory :

  It contains one entry per sub-flow. a 'sub-flow' is a unique path from
  Header Parser to the flow table. Multiple sub-flows can point to the
  same 'flow' (each flow has an id from 8 to 29, which is its index in the
  Lookup Id table) :

  - .../flows/00/...
             /01/...
             ...
             /51/id : The flow id. There are 21 unique flows. There's one
                       flow per combination of the following parameters :
                       - L4 protocol (TCP, UDP, none)
                       - L3 protocol (IPv4, IPv6)
                       - L3 parameters (Fragmented or not)
                       - L2 parameters (Vlan tag presence or not)
              .../type : The flow type. This is an even higher level flow,
                         that we manipulate with ethtool. It can be :
                         "udp4" "tcp4" "udp6" "tcp6" "ipv4" "ipv6" "other".
              .../eth0/...
              .../eth1/engine : The hash generation engine used for this
	                        flow on the given port
                  .../hash_opts : The hash generation options indicating on
                                  what data we base the hash (vlan tag, src
                                  IP, src port, etc.)

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