bootstat: add shutdown,thermal,battery

Test: system/core/bootreason/boot_reason_test.sh
Bug: 63736262
Change-Id: I30d6b5308fd8616eae31ad13e925d66c9fc07367
diff --git a/bootstat/bootstat.cpp b/bootstat/bootstat.cpp
index d1fe9c7..c1d799e 100644
--- a/bootstat/bootstat.cpp
+++ b/bootstat/bootstat.cpp
@@ -224,6 +224,7 @@
     {"reboot,by_key", 84},
     {"reboot,longkey", 85},
     {"reboot,2sec", 86},
+    {"shutdown,thermal,battery", 87},
 };
 
 // Converts a string value representing the reason the system booted to an