net/mlx5: update eCPRI flex parser structures

net/mlx5: update eCPRI flex parser structures

To handle eCPRI protocol in the flows the mlx5 PMD engages
flex parser hardware feature. While we were implementing
eCPRI support we anticipated the flex parser usage extension,
and all related variables were named accordingly, containing
flex syllabus. Now we are preparing to introduce more common
approach of flex item, in order to avoid naming conflicts
and improve the code readability the eCPRI infrastructure
related variables are renamed as preparation step.

Later, once we have the new flex item implemented, we could
consider to refactor the eCPRI protocol support  to move on
common flex item basis.

Signed-off-by: Viacheslav Ovsiienko <viacheslavo@nvidia.com>