PEL: Convert a BCDTime to epoch milliseconds

Add a new function to convert a BCDTime value from a PEL to the number
of milliseconds since the epoch.

This will be used to put the PEL creation timestamp on D-Bus.

Signed-off-by: Matt Spinler <spinler@us.ibm.com>
Change-Id: Ic470c9324e959b3e6a7eea29db4162a45dd54fc3
diff --git a/test/openpower-pels/pel_manager_test.cpp b/test/openpower-pels/pel_manager_test.cpp
index 36b1d14..4352153 100644
--- a/test/openpower-pels/pel_manager_test.cpp
+++ b/test/openpower-pels/pel_manager_test.cpp
@@ -503,7 +503,7 @@
 // An ESEL from the wild
 const std::string esel{
     "00 00 df 00 00 00 00 20 00 04 12 01 6f aa 00 00 "
-    "50 48 00 30 01 00 33 00 00 00 00 07 5c 69 cc 0d 00 00 00 07 5c d5 50 db "
+    "50 48 00 30 01 00 33 00 20 23 05 11 10 20 20 00 00 00 00 07 5c d5 50 db "
     "42 00 00 10 00 00 00 00 00 00 00 00 00 00 00 00 90 00 00 4e 90 00 00 4e "
     "55 48 00 18 01 00 09 00 8a 03 40 00 00 00 00 00 ff ff 00 00 00 00 00 00 "
     "50 53 00 50 01 01 00 00 02 00 00 09 33 2d 00 48 00 00 00 e0 00 00 10 00 "