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/pid/pidloop.cpp b/pid/pidloop.cpp
index b86ea4b..56bf8bd 100644
--- a/pid/pidloop.cpp
+++ b/pid/pidloop.cpp
@@ -37,7 +37,7 @@
     // Run the margin PIDs.
     zone->processThermals();
     // Get the maximum RPM setpoint.
-    zone->determineMaxRPMRequest();
+    zone->determineMaxSetPointRequest();
 }
 
 void pidControlLoop(PIDZone* zone, boost::asio::steady_timer& timer, bool first,