mlxsw: core: Extend thermal core with per inter-connect device thermal zones

Add a dedicated thermal zone for each inter-connect device. The
current temperature is obtained from inter-connect temperature sensor
and the default trip points are set to the same values as default ASIC
trip points. These settings could be changed from the user space.
A cooling device (fan) is bound to all inter-connect devices.

Signed-off-by: Vadim Pasternak <vadimp@mellanox.com>
Signed-off-by: Ido Schimmel <idosch@mellanox.com>
Acked-by: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>