ART: Introduce Mips32 R6

Add an instruction-set feature for Mips R6. Currently restricted
to the interpreter.

Change-Id: Ic6d888e135bc87340229a0543dd94d0c1e863edd
diff --git a/runtime/elf_utils.h b/runtime/elf_utils.h
index 7b00bad..3579e27 100644
--- a/runtime/elf_utils.h
+++ b/runtime/elf_utils.h
@@ -30,6 +30,7 @@
 #define EF_ARM_EABI_VER5 0x05000000
 #define EF_MIPS_ABI_O32 0x00001000
 #define EF_MIPS_ARCH_32R2 0x70000000
+#define EF_MIPS_ARCH_32R6 0x90000000
 
 #define EI_ABIVERSION 8
 #define EM_ARM 40