[AArch64] Gas add BFD_RELOC_AARCH64_LD64_GOTOFF_LO15 support

[AArch64] Gas add BFD_RELOC_AARCH64_LD64_GOTOFF_LO15 support

2015-06-15  Renlin Li <renlin.li@arm.com>
bfd/
    * reloc.c (BFD_RELOC_AARCH64_LD64_GOTOFF_LO15): New entry.
    * elfnn-aarch64.c (elfNN_aarch64_howto_table): New entry for
    BFD_RELOC_AARCH64_LD64_GOTOFF_LO15.
    * bfd-in2.h: Regenerate.
    * libbfd.h: Regenerate.

gas/
    * config/tc-aarch64.c (reloc_table): New relocation modifier.
    (md_apply_fix): Support BFD_RELOC_AARCH64_LD64_GOTOFF_LO15.
    (aarch64_force_relocation): Ditto

gas/testsuite/
    * gas/aarch64/reloc-insn.s: Update test
    * gas/aarch64/reloc-insn.d: Update expected result.