Add implicit null pointer and stack overflow checks for Mips.

Bug: 21555893
Change-Id: I2a995be128a5603d08753c14956dd8c8240ac63c
diff --git a/dex2oat/dex2oat.cc b/dex2oat/dex2oat.cc
index b4520e9..677ff0d 100644
--- a/dex2oat/dex2oat.cc
+++ b/dex2oat/dex2oat.cc
@@ -975,6 +975,8 @@
       case kArm64:
       case kX86:
       case kX86_64:
+      case kMips:
+      case kMips64:
         implicit_null_checks = true;
         implicit_so_checks = true;
         break;