commonlib: Add essential comments for ELOG_CROS_DIAG_RESULT

ELOG_CROS_DIAG_RESULT_* codes should be consistent with the enum
definition of enumerated histograms.

Hence add comments based on the requirements of enum histograms in
histogram guidelines.

BUG=b:4047421
TEST=none

Change-Id: I1a1a7c863d5aa9496649f81dc94fd79a6ad482df
Signed-off-by: Hsuan Ting Chen <roccochen@chromium.org>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/70145
Reviewed-by: Yu-Ping Wu <yupingso@google.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
diff --git a/src/commonlib/bsd/include/commonlib/bsd/elog.h b/src/commonlib/bsd/include/commonlib/bsd/elog.h
index 06ea5a7..1f39090 100644
--- a/src/commonlib/bsd/include/commonlib/bsd/elog.h
+++ b/src/commonlib/bsd/include/commonlib/bsd/elog.h
@@ -316,7 +316,12 @@
 #define   ELOG_CROS_DIAG_TYPE_STORAGE_TEST_EXTENDED 0x03
 #define   ELOG_CROS_DIAG_TYPE_MEMORY_QUICK          0x04
 #define   ELOG_CROS_DIAG_TYPE_MEMORY_FULL           0x05
-/* Result codes for elog_event_cros_diag_log in ELOG_CROS_DIAGNOSTICS_LOGS */
+/*
+ * Result codes for elog_event_cros_diag_log in ELOG_CROS_DIAGNOSTICS_LOGS
+ *
+ * These values are persisted to logs. Entries should not be renumbered and
+ * numeric values should never be reused.
+ */
 #define   ELOG_CROS_DIAG_RESULT_PASSED              0x01
 #define   ELOG_CROS_DIAG_RESULT_ERROR               0x02
 #define   ELOG_CROS_DIAG_RESULT_FAILED              0x03