[llvm-readelf] - Don't print OS/Processor specific prefix for known ELF file types.

[llvm-readelf] - Don't print OS/Processor specific prefix for known ELF file types.

This is a change suggested in post commit comments for
D93096 (https://reviews.llvm.org/D93096#2451796).

Imagine we want to add a custom OS specific ELF file type.
For that we can update the `ElfObjectFileType` array:

```
static const EnumEntry<unsigned> ElfObjectFileType[] = {
...
  {"Core",         "CORE (Core file)",         ELF::ET_CORE},
  {"MyType",       "MyType (my description)",     0xfe01},
};
```

The current code then might print:
```
OS Specific: (MyType (my description))
```

Though instead we probably would like to see a nicer output, e.g:
```
Type: MyType (my description)
```

To achieve that we can reorder the code slightly.

It is impossible to add a test I think, because we have no custom values in
the `ElfObjectFileType` array in LLVM.

Differential revision: https://reviews.llvm.org/D93217