Add test case to test MSA feature for i6400 and i6500 MIPS cpus

Also remove codegen test i6500.ll

Author: mgoudar

clang/test/Driver/mips-cpus.c

@@ -0,0 +1,9 @@
+// Check target CPUs are correctly passed.
+
+// RUN: %clang --target=mips64 -### -c %s 2>&1 -mcpu=i6400 -mmsa | FileCheck -check-prefix=MCPU-I6400 %s
+// MCPU-I6400: "-target-cpu" "i6400"
+// MCPU-I6400-SAME: "-target-feature" "+msa"
+
+// RUN: %clang --target=mips64 -### -c %s 2>&1 -mcpu=i6500 -mmsa | FileCheck -check-prefix=MCPU-I6500 %s
+// MCPU-I6500: "-target-cpu" "i6500"
+// MCPU-I6500-SAME: "-target-feature" "+msa"