[PATCH] powerpc: Fix old g5 issues with windfarm

Some of the windfarm sensor modules can initialize on old machines that
don't have full windfarm support like non-dual core desktop G5s.
Unfortunately, by doing so, they would trigger a bug in their matching
algorithm causing them to attach to the wrong bus, thus triggering
issues with the i2c core and breaking the thermal driver.

This patch fixes the probing issue (so that they will work when a
windfarm port is done to these machines) and also prevents for now
windfarm to load at all on these machines that still use therm_pm72 to
avoid wasting resources.

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Paul Mackerras <paulus@samba.org>