i2c: piix4: Add support for secondary SMBus on AMD SB800 and AMD FCH chipsets

Add support for the secondary SMBus controller on the AMD SB800 and AMD FCH
chipsets.

Signed-off-by: Rudolf Marek <r.marek@assembler.cz>
Tested-by: Paul Menzel <paulepanter@users.sourceforge.net>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>