PEL: Support for going between PELs & registry

Add tables that allow one to go between how a PEL field actually shows
up in the PEL (raw bytes) and how it shows up in the message registry (a
string enumeration).  The tables also have a column to show a string
description of that value that can be used by the parser, though for now
those descriptions are all left at "TODO".

There only needs to be a table for a PEL field when there is a
corresponding message registry field that is a string enumeration, so
that when code looks up an error in the message registry it knows what
to fill in the PEL with.

Also provide APIs to look up a row in the table by either the PEL value
or the message registry value.

Signed-off-by: Matt Spinler <spinler@us.ibm.com>
Change-Id: Iac849bcd2b0449a8d03fac7eb067484e91d28259
diff --git a/extensions/openpower-pels/openpower-pels.mk b/extensions/openpower-pels/openpower-pels.mk
index 4f424f7..14e1966 100644
--- a/extensions/openpower-pels/openpower-pels.mk
+++ b/extensions/openpower-pels/openpower-pels.mk
@@ -8,6 +8,7 @@
 	extensions/openpower-pels/mtms.cpp \
 	extensions/openpower-pels/paths.cpp \
 	extensions/openpower-pels/pel.cpp \
+	extensions/openpower-pels/pel_values.cpp \
 	extensions/openpower-pels/private_header.cpp \
 	extensions/openpower-pels/repository.cpp \
 	extensions/openpower-pels/user_header.cpp