PEL: OpenBMC event log sev to PEL sev helper

Add a function to map the OpenBMC event log severity values to PEL
severity values.

When creating a PEL from an OpenBMC event log, the event log will have
its own severity property, and if the PEL message registry entry for
that error doesn't supply its own severity (it's optional), use this
function to come up with the PEL severity value to use.

Signed-off-by: Matt Spinler <spinler@us.ibm.com>
Change-Id: I66aa001265d8acadb165de874e4ade03a8e28007
diff --git a/extensions/openpower-pels/openpower-pels.mk b/extensions/openpower-pels/openpower-pels.mk
index aa69a2e..89143b2 100644
--- a/extensions/openpower-pels/openpower-pels.mk
+++ b/extensions/openpower-pels/openpower-pels.mk
@@ -12,4 +12,5 @@
 	extensions/openpower-pels/private_header.cpp \
 	extensions/openpower-pels/registry.cpp \
 	extensions/openpower-pels/repository.cpp \
+	extensions/openpower-pels/severity.cpp \
 	extensions/openpower-pels/user_header.cpp