rename away from RPM

The SetPoint output from a thermal PID is likely RPM, and that value is
then fed into a fan controller PID as the set-point (unit: RPM).  This
does not have to be RPM, however.  Continue renaming variables and
methods to remove the explicit unit-naming.

Signed-off-by: Patrick Venture <venture@google.com>
Change-Id: I570dee0c688338f9a458cac7123314717bee2b42
diff --git a/conf.hpp b/conf.hpp
index 35c2da5..95bdeaa 100644
--- a/conf.hpp
+++ b/conf.hpp
@@ -48,7 +48,7 @@
  */
 struct ZoneConfig
 {
-    /* The minimum RPM value we would ever want. */
+    /* The minimum set-point value we would ever want (typically in RPM) */
     double minThermalOutput;
 
     /* If the sensors are in fail-safe mode, this is the percentage to use. */