devlink: Create generic devlink health reporter search function

Add a generic __devlink_health_reporter_find_by_name() that can be used
with arbitrary devlink health reporter list.

Signed-off-by: Vladyslav Tarasiuk <vladyslavt@mellanox.com>
Reviewed-by: Moshe Shemesh <moshe@mellanox.com>
Reviewed-by: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>