MIPS[64]: Fix issue with mjsunit/wasm/multi-value

Added return value registers on both MIPS32 and MIPS 64.

Bug: 
Change-Id: I3199a73f90ef7b0bc9e18d716fcdf4c8c479f7fd
Reviewed-on: https://chromium-review.googlesource.com/774286Reviewed-by: Andreas Haas <ahaas@chromium.org>
Commit-Queue: Ivica Bogosavljevic <ivica.bogosavljevic@mips.com>
Cr-Commit-Position: refs/heads/master@{#49438}

src/compiler/wasm-linkage.cc

@@ -83,7 +83,7 @@ LinkageLocation stackloc(int i, MachineType type) {
 // == mips ===================================================================
 // ===========================================================================
 #define GP_PARAM_REGISTERS a0, a1, a2, a3
-#define GP_RETURN_REGISTERS v0, v1
+#define GP_RETURN_REGISTERS v0, v1, t7
 #define FP_PARAM_REGISTERS f2, f4, f6, f8, f10, f12, f14
 #define FP_RETURN_REGISTERS f2, f4
 
@@ -92,7 +92,7 @@ LinkageLocation stackloc(int i, MachineType type) {
 // == mips64 =================================================================
 // ===========================================================================
 #define GP_PARAM_REGISTERS a0, a1, a2, a3, a4, a5, a6, a7
-#define GP_RETURN_REGISTERS v0, v1
+#define GP_RETURN_REGISTERS v0, v1, t3
 #define FP_PARAM_REGISTERS f2, f4, f6, f8, f10, f12, f14
 #define FP_RETURN_REGISTERS f2, f4