ethdev: allow negative values in flow rule types

ethdev: allow negative values in flow rule types

RTE flow items & actions use positive values in item & action type.
Negative values are reserved for PMD private types. PMD
items & actions usually are not exposed to application and are not
used to create RTE flows.

The patch allows applications with access to PMD flow
items & actions ability to integrate RTE and PMD items & actions
and use them to create flow rule.

RTE flow item or action conversion library accepts positive known
element types with predefined sizes only. Private PMD items and
actions do not fit into this scheme because PMD type values are
negative, each PMD has it's own types numeration and element types and
their sizes are not visible at RTE level.  To resolve these
limitations the patch proposes this solution:
1. PMD can expose elements of pointer size only.  RTE flow
   conversion functions will use pointer size for each configuration
   object in private PMD element it processes;
2. RTE flow verification will not reject elements with negative type.

Signed-off-by: Gregory Etelson <getelson@nvidia.com>
Acked-by: Ori Kam <orika@nvidia.com>
Acked-by: Viacheslav Ovsiienko <viacheslavo@nvidia.com>