[PATCH] [ARM] Remove references to redundant cortex-a9-mp CPU

[Charlie Turner]

>>! In D6118#4, @rengolin wrote:
> I can't remember now, does that mean that "-mcpu=cortex-a9-mp" will work and mean "arm7tdmi" or will it fail with "unknown CPU"?

It does fail,

```
$ clang -target arm-none-eabi -mcpu=cortex-a9-mp test.ll 
error: unknown target CPU 'cortex-a9-mp'
```

> I'm actually surprised that we had no tests for it. :)

So was I! :)

Thank you for reviewing,
Charlie.

http://reviews.llvm.org/D6118