hwmon: fam15h_power: fix bogus values with current BIOSes

hwmon: fam15h_power: fix bogus values with current BIOSes

Newer BKDG[1] versions recommend a different initialization value for
the running average range register in the northbridge. This improves
the power reading by avoiding counter saturations resulting in bogus
values for anything below about 80% of TDP power consumption.
Updated BIOSes will have this new value set up from the beginning,
but meanwhile we correct this value ourselves.
This needs to be done on all northbridges, even on those where the
driver itself does not register at.

This fixes the driver on all current machines to provide proper
values for idle load.

[1]
http://support.amd.com/us/Processor_TechDocs/42301_15h_Mod_00h-0Fh_BKDG.pdf
Chapter 3.8: D18F5xE0 Processor TDP Running Average (p. 452)

Signed-off-by: Andre Przywara <andre.przywara@amd.com>
Acked-by: Jean Delvare <khali@linux-fr.org>
[guenter.roeck@ericsson.com: Removed unnecessary return statement]
Signed-off-by: Guenter Roeck <guenter.roeck@ericsson.com>
Cc: stable@vger.kernel.org # 3.0+