SB Temperature Sensor Interface (SB-TSI) is an SMBus compatible
interface that reports AMD SoC's Ttcl (normalized temperature),
and resembles a typical 8-pin remote temperature sensor's I2C interface
to BMC.

This commit adds basic support using this interface to read CPU
temperature, and read/write high/low CPU temp thresholds.

To instantiate this driver on an AMD CPU with SB-TSI
support, the i2c bus number would be the bus connected from the board
management controller (BMC) to the CPU. The i2c address is specified in
Section 6.3.1 of the spec [1]: The SB-TSI address is normally 98h for
socket 0 and 90h for socket 1, but it could vary based on hardware address
select pins.

[1]: https://www.amd.com/system/files/TechDocs/56255_OSRR.pdf

Test status: tested reading temp1_input, and reading/writing
temp1_max/min.
Signed-off-by: Kun Yi <kunyi@google.com>
Link: https://lore.kernel.org/r/20201211215427.3281681-2-kunyi@google.comSigned-off-by: Guenter Roeck <linux@roeck-us.net>