net/mlx5: extend flow mark support

Flow MARK item is newly supported along with MARK action. MARK
action and item are supported on both Rx and Tx. It works on the
metadata reg_c[] only if extensive flow metadata register is
supported. Without the support, MARK action behaves same as
before - valid only on Rx and no MARK item is valid.

FLAG action is also modified accordingly. FLAG action is
supported on both Rx and Tx via reg_c[] if extensive flow
metadata register is supported.

However, the new MARK/FLAG item and action are currently
disabled until register copy on loopback is supported by
forthcoming patches.

The actual index of engaged metadata reg_c[] register to
support FLAG/MARK actions depends on dv_xmeta_en devarg value.

For extensive metadata mode 1 the reg_c[1] is used and
transitive MARK data width is 24. For extensive metadata mode 2
the reg_c[0] is used and transitive MARK data width might be
restricted to 0 or 16 bits, depending on kernel usage of reg_c[0].
The actual supported width can be discovered by series of trials
with rte_flow_validate().

Signed-off-by: Yongseok Koh <yskoh@mellanox.com>
Signed-off-by: Viacheslav Ovsiienko <viacheslavo@mellanox.com>
Acked-by: Matan Azrad <matan@mellanox.com>