net/mlx5e: Declare bitmap using kernel macro

Replace explicit declaration of bitmap with DECLARE_BITMAP kernel macro.

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