BPF relocations review / refactoring

BPF relocations review / refactoring

- Removed not needed relocations.
- Renamed relocations to match llvm and linux kernel.

Relocation changes:
  R_BPF_INSN_64 	=> R_BPF_64_64
  R_BPF_INSN_DISP32 	=> R_BPF_64_32
  R_BPF_DATA_32 	=> R_BPF_64_ABS32
  R_BPF_DATA_64 	=> R_BPF_64_ABS64

ChangeLog:

  * bfd/bpf-reloc.def: Created file with BPF_HOWTO macro entries.
  * bfd/reloc.c: Removed non needed relocations.
  * bfd/bfd-in2.h: regenerated.
  * bfd/libbfd.h: regenerated.
  * bfd/elf64-bpf.c: Changed relocations.
  * include/elf/bpf.h: Adapted relocation values/names.
  * gas/config/tc-bpf.c: Changed relocation mapping.