mlxsw: reg: Extend MTMP register with new threshold field

Extend Management Temperature (MTMP) register with new field specifying
the maximum temperature threshold.

Extend mlxsw_reg_mtmp_unpack() function with two extra arguments,
providing high and maximum temperature thresholds. For modules, these
thresholds correspond to critical and emergency thresholds that are read
from the module's EEPROM.

Signed-off-by: Mykola Kostenok <c_mykolak@nvidia.com>
Acked-by: Vadim Pasternak <vadimp@nvidia.com>
Signed-off-by: Ido Schimmel <idosch@nvidia.com>
Signed-off-by: David S. Miller <davem@davemloft.net>