net/mlx5: Remove redundant EQ API exports

EQ structure and API is private to mlx5_core driver only, external
drivers should not have access or the means to manipulate EQ objects.

Remove redundant exports and move API functions out of the linux/mlx5
include directory into the driver's mlx5_core.h private include file.

Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>
Reviewed-by: Gal Pressman <galp@mellanox.com>