elog: Add event type for CPU thermal trip

There is a status bit for this event in most intel chipsets that
we can read and report.  Start by adding the new event type.

BUG=chrome-os-partner:28234
TEST=build and boot on wtm2

Change-Id: Ib06411e3b87a1d069fb469943dd445bee6c1291f
Signed-off-by: Duncan Laurie <dlaurie@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/199370
Reviewed-by: Aaron Durbin <adurbin@chromium.org>

src/include/elog.h

@@ -143,6 +143,9 @@ struct elog_event_data_me_extended {
 /* EC Shutdown Reason */
 #define ELOG_TYPE_EC_SHUTDOWN             0xa5
 
+/* CPU Thermal Trip */
+#define ELOG_TYPE_THERM_TRIP              0xa7
+
 #if CONFIG_ELOG
 /* Eventlog backing storage must be initialized before calling elog_init(). */
 extern int elog_init(void);