readelf: Support RELR in -S and -d and output

readelf -r dumping support is not added in this patch.

include/
	* elf/common.h: Add SHT_RELR, DT_RELR{,SZ,ENT}
bfd/
	* elf.c (_bfd_elf_print_private_bfd_data): Add DT_RELR{,SZ,ENT}.
binutils/
	* readelf.c (get_dynamic_type): Add DT_RELR{,SZ,ENT}.
	(get_section_type_name): Add SHT_RELR.