mlxsw: core: Extend the index size for temperature sensors readout

Extend sensor index size for Management Temperature Bulk Register
(MTBR) and Management Temperature Register (MTMP) upto 12 bits in
order to align registers description with new version of PRM document.
Add define for base sensor index for SFP modules temperature reading
for MTMP register.

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