net/mlx5: extend flow metadata support

net/mlx5: extend flow metadata support

META item is supported on both Rx and Tx. 'transfer' attribute
is also supported. SET_META action is also added.

Due to restriction on reg_c[meta], various bit width might be
available. If devarg parameter dv_xmeta_en=1, the META uses
metadata register reg_c[0], which may be required for internal
kernel or firmware needs. In this case PMD queries kernel about
available fields in reg_c[0] and restricts the register usage
accordingly. If devarg parameter dv_xmeta_en=2, the META feature
uses reg_c[1], there should be no limitations on the data width.

However, extensive MEAT feature is currently disabled until
register copy on loopback is supported by forthcoming patches.

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