Recipes for installing fan zone yaml

Provides the virtual/phosphor-fan-control-zone-config virtual.

By default, it will install an empty zones.yaml file into the
directory needed by the phosphor-fan-control compile.

To provide a system specific fan zone yaml, put one in that system's
layer and install it with a .bbappend, which is what is being done
in this commit for Witherspoon.

Change-Id: Ie58fc9eb7b39cecffa39905266542bae16c0f977
Signed-off-by: Matt Spinler <spinler@us.ibm.com>
diff --git a/classes/phosphor-fan.bbclass b/classes/phosphor-fan.bbclass
index b59f1f5..198b292 100644
--- a/classes/phosphor-fan.bbclass
+++ b/classes/phosphor-fan.bbclass
@@ -1 +1,2 @@
 presence_datadir="${datadir}/phosphor-fan-presence"
+control_datadir="${datadir}/phosphor-fan-control"