nfp: dump single hwinfo field by key

- Add spec TLV for hwinfo field, containing key string as data.
- Add dump TLV for hwinfo field, with data being key and value as packed
  zero-terminated strings.
- If specified hwinfo field is not found, dump the spec TLV as -ENOENT
  error.

Signed-off-by: Carl Heymann <carl.heymann@netronome.com>
Reviewed-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Signed-off-by: Simon Horman <simon.horman@netronome.com>
Signed-off-by: David S. Miller <davem@davemloft.net>