regex/mlx5: fix registered driver name

regex/mlx5: fix registered driver name

The driver name was registered as "net_mlx5_regex".
It is renamed as "regex_mlx5".
The same name is used in mlx5_regex_driver.pci_driver.driver.name,
instead of "mlx5_regex", for consistency.

The string used for log registration (pmd.regex.mlx5) could be derived
from the driver name. A macro is created so name definitions are close.

Fixes: cfc672a90b74 ("regex/mlx5: support probing")

Signed-off-by: Thomas Monjalon <thomas@monjalon.net>
Acked-by: Ori Kam <orika@mellanox.com>