AArch64/ARM64: disentangle the "B.CC" and "LDR lit" operands

These can have different relocations in ELF. In particular both:

    b.eq global
    ldr x0, global

are valid, giving different relocations. The only possible way to distinguish
them is via a different fixup, so the operands had to be separated throughout
the backend.

llvm-svn: 207105