MIPS64: Improve string and class loads.

This adds most kinds of string/class loads.
JIT string/class loads are TBD separately.

This also fixes Mips64Assembler::LoadLabelAddress()
(adding a constant to a 64-bit address must be done
using daddiu, not addiu).

Test: test-art-host-gtest
Test: booted MIPS64 (with 2nd arch MIPS32R6) in QEMU
Test: "make -j1 ART_TEST_DEFAULT_COMPILER=false ART_TEST_OPTIMIZING=true
       ART_TEST_INTERPRETER=false ART_TEST_JIT=false
       ART_TEST_PIC_TEST=true test-art-target-run-test64"

Change-Id: I1f94ece4cd202382c11167e1ed958e9d08d92822
diff --git a/compiler/linker/mips64/relative_patcher_mips64_test.cc b/compiler/linker/mips64/relative_patcher_mips64_test.cc
index 9e37f6b..c317058 100644
--- a/compiler/linker/mips64/relative_patcher_mips64_test.cc
+++ b/compiler/linker/mips64/relative_patcher_mips64_test.cc
@@ -45,7 +45,7 @@
 
 const uint8_t Mips64RelativePatcherTest::kUnpatchedPcRelativeRawCode[] = {
     0x34, 0x12, 0x5E, 0xEE,  // auipc s2, high(diff); placeholder = 0x1234
-    0x78, 0x56, 0x52, 0x26,  // addiu s2, s2, low(diff); placeholder = 0x5678
+    0x78, 0x56, 0x52, 0x66,  // daddiu s2, s2, low(diff); placeholder = 0x5678
 };
 const uint8_t Mips64RelativePatcherTest::kUnpatchedPcRelativeCallRawCode[] = {
     0x34, 0x12, 0x3E, 0xEC,  // auipc at, high(diff); placeholder = 0x1234
@@ -71,7 +71,7 @@
 
   const uint8_t expected_code[] = {
       static_cast<uint8_t>(diff >> 16), static_cast<uint8_t>(diff >> 24), 0x5E, 0xEE,
-      static_cast<uint8_t>(diff), static_cast<uint8_t>(diff >> 8), 0x52, 0x26,
+      static_cast<uint8_t>(diff), static_cast<uint8_t>(diff >> 8), 0x52, 0x66,
   };
   EXPECT_TRUE(CheckLinkedMethod(MethodRef(1u), ArrayRef<const uint8_t>(expected_code)));
 }