nfp: add support for NFDK data path

Add new data path.  The TX is completely different, each packet
has multiple descriptor entries (between 2 and 32).  TX ring is
divided into blocks 32 descriptor, and descritors of one packet
can't cross block bounds. The RX side is the same for now.

ABI version 5 or later is required.  There is no support for
VLAN insertion on TX. XDP_TX action and AF_XDP zero-copy is not
implemented in NFDK path.

Changes to Jakub's work:
* Move statistics of hw_csum_tx after jumbo packet's segmentation.
* Set L3_CSUM flag to enable recaculating of L3 header checksum
in ipv4 case.
* Mark the case of TSO a packet with metadata prepended as
unsupported.

Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Signed-off-by: Xingfeng Hu <xingfeng.hu@corigine.com>
Signed-off-by: Yinjun Zhang <yinjun.zhang@corigine.com>
Signed-off-by: Dianchao Wang <dianchao.wang@corigine.com>
Signed-off-by: Fei Qin <fei.qin@corigine.com>
Signed-off-by: Simon Horman <simon.horman@corigine.com>
Signed-off-by: David S. Miller <davem@davemloft.net>