Add tach trust groups to witherspoon monitor YAML

These will be used to specify that the 2nd rotor tach values
shouldn't be trusted when all of them are zero, because
that just means the fans are moving to a new target.

Resolves openbmc/openbmc#2336

Change-Id: I4b2ca6bb732d214dca67096817612025e1319226
Signed-off-by: Matt Spinler <spinler@us.ibm.com>
1 file changed