PowerPC TPREL reloc handling

PowerPC TPREL reloc handling

Tidy how these are handled in PIEs.

	* elf32-ppc.c (must_be_dyn_reloc): Use bfd_link_dll.  Comment.
	(ppc_elf_check_relocs): Only set DF_STATIC_TLS in shared libs.
	(ppc_elf_relocate_section): Comment fix.
	* elf64-ppc.c (must_be_dyn_reloc): Use bfd_link_dll.  Comment.
	(ppc64_elf_check_relocs): Only set DF_STATIC_TLS in shared libs.
	Support dynamic relocs for TPREL16 when non-pic too.
	(dec_dynrel_count): Adjust TPREL16 handling as per check_relocs.
	(ppc64_elf_relocate_section): Support dynamic relocs for TPREL16
	when non-pic too.