mlxsw: core: Modify thermal zone definition

Modify thermal zone trip points setting for better alignment with system
thermal requirement.

Add hysteresis thresholds for thermal trips in order to avoid throttling
around thermal trip point. If hysteresis temperature is not considered,
PWM can have side effect of flip up/down on thermal trip point boundary.

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