Add kMips and mips32r2 target attribute. Remove NoFramePointerElim.

MIPS ICS devices today are mips32r2. Tested LLVM on MIPS devices without
synci and rdhwr instructions to make sure LLVM/mips32r2 is working.

Change-Id: If1db7fe268e9f3b7d27eedbacd1d55620d57612a
diff --git a/src/constants.h b/src/constants.h
index 5c1323f..bb17c2d 100644
--- a/src/constants.h
+++ b/src/constants.h
@@ -25,7 +25,8 @@
   kNone,
   kArm,
   kThumb2,
-  kX86
+  kX86,
+  kMips
 };
 
 enum InvokeType {