[llvm][ARM/AArch64] Convert Target Parser CPU tests to fixtures

Also convert the test function to use EXPECT_EQ and
remove the special case for the AEK_NONE extension.

This means that each test is marked as failing separatley
and the accumultated EXPECT failures are printed next
to that test, with its parameters.

Before they would be hidden by the "pass &=" pattern
and failures would print in one block since it was a
"single" test.

Example of the new failure messages:
```
ARMCPUTestsPart1/ARMCPUTestFixture.ARMCPUTests/6
[==========] Running 1 test from 1 test case.
[----------] Global test environment set-up.
[----------] 1 test from ARMCPUTestsPart1/ARMCPUTestFixture
[ RUN      ] ARMCPUTestsPart1/ARMCPUTestFixture.ARMCPUTests/6
/work/open_source/nightly-llvm/llvm-project/llvm/unittests/Support/TargetParserTest.cpp:66:
Failure
      Expected: params.ExpectedFlags
      Which is: 3405705229
To be equal to: default_extensions
      Which is: 1
[  FAILED  ] ARMCPUTestsPart1/ARMCPUTestFixture.ARMCPUTests/6, where
GetParam() = "arm8", "armv4", "none", 0xcafef00d, "4" (0 ms)
```

Reviewed By: MarkMurrayARM

Differential Revision: https://reviews.llvm.org/D93392