[llvm][AArch64] Actually check expected FPU for CPUs

[DavidSpickett]

Summary

We were passing this as an argument but never using
it. ARM has always checked this.

Note that the FPU list is shared between ARM and AArch64
so there is no AArch64::getFPUName, just ARM::getFPUName.

[dmgreen]

Sounds good to me.

llvm/unittests/Support/TargetParserTest.cpp

 //===----------- TargetParser.cpp - Target Parser -------------------------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 
bool testAArch64CPU(StringRef CPUName, StringRef ExpectedArch,
   bool pass = AArch64::getArchName(AK).equals(ExpectedArch);
 
   uint64_t ExtKind = AArch64::getDefaultExtensions(CPUName, AK);
   if (ExtKind > 1 && (ExtKind & AArch64::AEK_NONE))
     pass &= ((ExtKind ^ AArch64::AEK_NONE) == ExpectedFlags);
   else
     pass &= (ExtKind == ExpectedFlags);
 
+  unsigned FPUKind = AArch64::getDefaultFPU(CPUName, AK);
+  pass &= ARM::getFPUName(FPUKind).equals(ExpectedFPU);
+
   pass &= AArch64::getCPUAttr(AK).equals(CPUAttr);
 
   return pass;
 }
 
 TEST(TargetParserTest, testAArch64CPU) {
   EXPECT_TRUE(testAArch64CPU(
       "invalid", "invalid", "invalid",