DbusPidZone: Allow per-zone setpoint files during tuning
DbusPidZone: Allow per-zone setpoint files during tuning

In tuning mode, in addition to the overall setpoint file,
also check for the existence of per-zone setpoint files.

If they exist, and contain a parseable RPM number,
they will be used. If both per-zone and overall files exist,
the per-zone will override the overall, appropriately for each zone.

Better error checking has been added,
detecting common user mistake of using PWM instead of RPM,
throttling error messages to avoid repetitive output.

Tested: It worked, here's an example...
echo 5000 > /etc/thermal.d/setpoint.zone0
echo 7000 > /etc/thermal.d/setpoint
echo 9000 > /etc/thermal.d/setpoint.zone2
Zone 0 will try for 5000 RPM, Zone 2 will try for 9000 RPM,
and Zone 1 (and all other zones) will try for 7000 RPM.

Signed-off-by: Josh Lehan <640cdef0d88764f22de94dce2c05fc22b037d36b@google.com>
Change-Id: Ic78d0fd2a0c32308356a0e2c7b03453416467c5b

openbmc/phosphor-pid-control,openbmc/phosphor-pid-control