i2c: piix4: Detect secondary SMBus controller on AMD AM4 chipsets

The AMD X370 and other AM4 chipsets (A/B/X 3/4/5 parts) and Threadripper
equivalents have a secondary SMBus controller at I/O port address
0x0B20.  This bus is used by several manufacturers to control
motherboard RGB lighting via embedded controllers.  I have been using
this bus in my OpenRGB project to control the Aura RGB on many
motherboards and ASRock also uses this bus for their Polychrome RGB
controller.

I am not aware of any CZ-compatible platforms which do not have the
second SMBus channel.  All of AMD's AM4- and Threadripper- series
chipsets that OpenRGB users have tested appear to have this secondary
bus.  I also noticed this secondary bus is present on older AMD
platforms including my FM1 home server.

Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=202587


Signed-off-by: Adam Honse <calcprogrammer1@gmail.com>
Reviewed-by: Jean Delvare <jdelvare@suse.de>
Reviewed-by: Sebastian Reichel <sebastian.reichel@collabora.com>
Tested-by: Sebastian Reichel <sebastian.reichel@collabora.com>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>