PEL: Validate the Action Flags field

According to the PEL spec, the Action Flags and Event Type fields in the
User Header section must be in agreement with the Severity field. So,
when a PEL is being created from an OpenBMC event log, check those
values for correctness and fix them up if required.

In addition, as those fields are optional in the message registry, this
code will also just set these two fields to valid values if they were
left out.

The rules being followed are documented in the PEL readme.

Signed-off-by: Matt Spinler <spinler@us.ibm.com>
Change-Id: Iad88de5080ba79a9ff31f962ef99bfc11994b9ed
diff --git a/extensions/openpower-pels/pel_rules.hpp b/extensions/openpower-pels/pel_rules.hpp
new file mode 100644
index 0000000..ca05875
--- /dev/null
+++ b/extensions/openpower-pels/pel_rules.hpp
@@ -0,0 +1,32 @@
+#pragma once
+
+#include <cstdint>
+#include <tuple>
+
+namespace openpower
+{
+namespace pels
+{
+namespace pel_rules
+{
+
+/**
+ * @brief Ensure certain PEL fields are in agreement, and fix them if they
+ *        aren't.  These rules are documented in the README.md in this
+ *        directory.
+ *
+ * Note: The message registry schema enforces that there are no undefined
+ *       bits set in these fields.
+ *
+ * @param[in] actionFlags - The current Action Flags value
+ * @param[in] eventType - The current Event Type value
+ * @param[in] severity - The current Severity value
+ *
+ * @return std::tuple<actionFlags, eventType> - The corrected values.
+ */
+std::tuple<uint16_t, uint8_t> check(uint16_t actionFlags, uint8_t eventType,
+                                    uint8_t severity);
+
+} // namespace pel_rules
+} // namespace pels
+} // namespace openpower