devlink: introduce the health reporter test command

Introduce a test command for health reporters. User might use this
command to trigger test event on a reporter if the reporter supports it.

Signed-off-by: Jiri Pirko <jiri@nvidia.com>
Signed-off-by: Ido Schimmel <idosch@nvidia.com>
Signed-off-by: David S. Miller <davem@davemloft.net>