Change how hwmon.pl is invoked for MRW systems

This minor tweak removes the need for MRW using systems
to append the phosphor-hwmon recipe in their layer.

Change-Id: I3d9dcfff452e26d191df37ae7d759c6c2c3f2cd4
Signed-off-by: Brad Bishop <bradleyb@fuzziesquirrel.com>
diff --git a/meta-phosphor/conf/distro/include/phosphor-defaults.inc b/meta-phosphor/conf/distro/include/phosphor-defaults.inc
index 64309d1..28e04ef 100644
--- a/meta-phosphor/conf/distro/include/phosphor-defaults.inc
+++ b/meta-phosphor/conf/distro/include/phosphor-defaults.inc
@@ -54,6 +54,13 @@
 PREFERRED_PROVIDER_virtual/obmc-user-mgmt ?= "obmc-phosphor-user"
 PREFERRED_PROVIDER_virtual/obmc-wsgihost ?= "phosphor-gevent"
 
+# phosphor-hwmon-config
+#
+# The phosphor-hwmon package can have its configuration generated
+# automatically if the MRW feature is enabled.
+VIRTUAL-RUNTIME_phosphor-hwmon-config ?= \
+    "${@cf_enabled(d, 'obmc-mrw', 'phosphor-hwmon-config-mrw')}"
+
 # virtual/phosphor-ipmi-fru-hostfw-config
 #
 # The phosphor-ipmi-fru application is data-driven and requires an input