ART: Make InstructionSet an enum class and add kLast.

Adding InstructionSet::kLast shall make it easier to encode
the InstructionSet in fewer bits using BitField<>. However,
introducing `kLast` into the `art` namespace is not a good
idea, so we change the InstructionSet to an enum class.
This also uncovered a case of InstructionSet::kNone being
erroneously used instead of vixl32::Condition::None(), so
it's good to remove `kNone` from the `art` namespace.

Test: m test-art-host-gtest
Test: testrunner.py --host --optimizing
Change-Id: I6fa6168dfba4ed6da86d021a69c80224f09997a6
diff --git a/compiler/jni/jni_cfi_test.cc b/compiler/jni/jni_cfi_test.cc
index 5b57718..236b5c0 100644
--- a/compiler/jni/jni_cfi_test.cc
+++ b/compiler/jni/jni_cfi_test.cc
@@ -102,13 +102,13 @@
   }
 };
 
-#define TEST_ISA(isa) \
-  TEST_F(JNICFITest, isa) { \
-    std::vector<uint8_t> expected_asm(expected_asm_##isa, \
-        expected_asm_##isa + arraysize(expected_asm_##isa)); \
-    std::vector<uint8_t> expected_cfi(expected_cfi_##isa, \
-        expected_cfi_##isa + arraysize(expected_cfi_##isa)); \
-    TestImpl(isa, #isa, expected_asm, expected_cfi); \
+#define TEST_ISA(isa)                                                 \
+  TEST_F(JNICFITest, isa) {                                           \
+    std::vector<uint8_t> expected_asm(expected_asm_##isa,             \
+        expected_asm_##isa + arraysize(expected_asm_##isa));          \
+    std::vector<uint8_t> expected_cfi(expected_cfi_##isa,             \
+        expected_cfi_##isa + arraysize(expected_cfi_##isa));          \
+    TestImpl(InstructionSet::isa, #isa, expected_asm, expected_cfi);  \
   }
 
 #ifdef ART_ENABLE_CODEGEN_arm