health_metric: add bmc metric path

Add the BMC health metric path to be used in phosphor-health-monitor.

Change-Id: I6a06fe12f7c89847a035a0e6b87dbdbad36cb708
Signed-off-by: Jagpal Singh Gill <paligill@gmail.com>
diff --git a/yaml/xyz/openbmc_project/Metric/Value.interface.yaml b/yaml/xyz/openbmc_project/Metric/Value.interface.yaml
index b00538f..bd01cac 100644
--- a/yaml/xyz/openbmc_project/Metric/Value.interface.yaml
+++ b/yaml/xyz/openbmc_project/Metric/Value.interface.yaml
@@ -107,3 +107,7 @@
                 Reboot statistic to track number of times device rebooted
                 because of a failure.
             value: reboot/count_with_failure
+    - name: BMC
+      description: >
+          The BMC metrics.
+      value: /xyz/openbmc_project/metric/bmc