Make the mips64r6 config pretend it has a 2nd arch

This fix buildbot's mips64 build. This is the same solution
as it is done in I5372c6a1d2e1e2462ef8671eef3a2337517ec0c8.

Change-Id: Ibe12cf7fbd9fc15a08ba984cf086302f175525f7
diff --git a/mips64r6/BoardConfig.mk b/mips64r6/BoardConfig.mk
index 47eb1d8..d656e66 100644
--- a/mips64r6/BoardConfig.mk
+++ b/mips64r6/BoardConfig.mk
@@ -20,11 +20,16 @@
 
 TARGET_CPU_ABI := mips64
 TARGET_CPU_SMP := true
-TARGET_CPU_VARIANT := generic
+TARGET_CPU_VARIANT := mips64r6
 TARGET_ARCH_VARIANT := mips64r6
 
 TARGET_PREFER_32_BIT_APPS :=
 TARGET_SUPPORTS_32_BIT_APPS :=
 TARGET_SUPPORTS_64_BIT_APPS := true
 
+TARGET_2ND_ARCH := mips
+TARGET_2ND_ARCH_VARIANT := mips32r2-fp
+TARGET_2ND_CPU_ABI := mips
+TARGET_2ND_CPU_VARIANT := mips32r2-fp
+
 USE_CLANG_PLATFORM_BUILD := true