Add keymaster_security_level_t for attestation.

Change-Id: Iffa71e3c285d35c2feafd04e8153306f086a3118
diff --git a/include/hardware/keymaster_defs.h b/include/hardware/keymaster_defs.h
index 046db52..e95850a 100644
--- a/include/hardware/keymaster_defs.h
+++ b/include/hardware/keymaster_defs.h
@@ -341,6 +341,11 @@
                                        * completeness. */
 } keymaster_verified_boot_t;
 
+typedef enum {
+    KM_SECURITY_LEVEL_SOFTWARE = 0,
+    KM_SECURITY_LEVEL_TRUSTED_ENVIRONMENT = 1,
+} keymaster_security_level_t;
+
 /**
  * Formats for key import and export.
  */