EpochTime: Add errors for properties

sdbusplus now supports errors on properties, so define the errors for
setting the Elapsed property.

The implementation depends on this to throw exceptions when error
occurs.

Change-Id: I2b22da8b038389b00288036aaa5601630583aaaa
Signed-off-by: Lei YU <mine260309@gmail.com>
diff --git a/xyz/openbmc_project/Time/EpochTime.interface.yaml b/xyz/openbmc_project/Time/EpochTime.interface.yaml
index 243802a..7b49fc0 100644
--- a/xyz/openbmc_project/Time/EpochTime.interface.yaml
+++ b/xyz/openbmc_project/Time/EpochTime.interface.yaml
@@ -7,4 +7,12 @@
           Time elpased since the
           Epoch(1 Jan 1970 00:00:00 UTC), in microseconds.
 
+          On setting this property, errors may be thrown.
+          InternalFailure means BMC fails to set the time.
+          InsufficientPermission means it is not allowed to set time depend
+          on the time settings.
+      errors:
+        - xyz.openbmc_project.Common.Error.InternalFailure
+        - xyz.openbmc_project.Common.Error.InsufficientPermission
+
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