Widen ELFYAML relocation type to 32 bits

The current 8 bits is sufficient for ELF32 targets but ELF64 requires
32 bits. Add a test for AArch64 that exposes the issue.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@222898 91177308-0d34-0410-b5e6-96231b3b80d8