[BFD, AArch64] Define elf_backend_fixup_gnu_properties in AArch64

[BFD, AArch64] Define elf_backend_fixup_gnu_properties in AArch64

This patch add support for elf_backend_fixup_gnu_properties for GNU
property support for AArch64. The new AArch64 specific definition
_bfd_aarch64_elf_link_fixup_gnu_properties goes through the property
list to find AArch64 type properties and removes the properties that
are marked as "property_remove".

*** bfd/ChangeLog ***

2019-03-20  Sudakshina Das  <sudi.das@arm.com>

	* elfxx-aarch64.c (_bfd_aarch64_elf_link_fixup_gnu_properties): Define.
	* elfxx-aarch64.h (_bfd_aarch64_elf_link_fixup_gnu_properties): Declare.
	(elf_backend_fixup_gnu_properties): Define for AArch64.