Add support for RISC-V architecture.

Add support for RISC-V architecture.

bfd	* Makefile.am: Add entries for riscv32-elf and riscv64-elf.
	* config.bdf: Likewise.
	* configure.ac: Likewise.
	* Makefile.in: Regenerate.
	* configure: Regenerate.
	* archures.c: Add bfd_riscv_arch.
	* reloc.c: Add riscv relocs.
	* targets.c: Add riscv_elf32_vec and riscv_elf64_vec.
	* bfd-in2.h: Regenerate.
	* libbfd.h: Regenerate.
	* elf-bfd.h: Add RISCV_ELF_DATA to enum elf_target_id.
	* elfnn-riscv.c: New file.
	* elfxx-riscv.c: New file.
	* elfxx-riscv.h: New file.

binutils* readelf.c (guess_is_rela): Add EM_RISCV.
	(get_machine_name): Likewise.
	(dump_relocations): Add support for riscv relocations.
	(get_machine_flags): Add support for riscv flags.
	(is_32bit_abs_reloc): Add R_RISCV_32.
	(is_64bit_abs_reloc): Add R_RISCV_64.
	(is_none_reloc): Add R_RISCV_NONE.
	* testsuite/binutils-all/objdump.exp (cpus_expected): Add riscv.
	Expect the debug_ranges test to fail.

gas	* Makefile.am: Add riscv files.
	* Makefile.in: Regenerate.
	* NEWS: Mention the support for this architecture.
	* configure.in: Define a default architecture.
	* configure: Regenerate.
	* configure.tgt: Add entries for riscv.
	* doc/as.texinfo: Likewise.
	* testsuite/gas/all/gas.exp: Expect the redef tests to fail.
	* testsuite/gas/elf/elf.exp: Expect the groupauto tests to fail.
	* config/tc-riscv.c: New file.
	* config/tc-riscv.h: New file.
	* doc/c-riscv.texi: New file.
	* testsuite/gas/riscv: New directory.
	* testsuite/gas/riscv/riscv.exp: New file.
	* testsuite/gas/riscv/t_insns.d: New file.
	* testsuite/gas/riscv/t_insns.s: New file.

ld	* Makefile.am: Add riscv files.
	* Makefile.in: Regenerate.
	* NEWS: Mention the support for this target.
	* configure.tgt: Add riscv entries.
	* emulparams/elf32lriscv-defs.sh: New file.
	* emulparams/elf32lriscv.sh: New file.
	* emulparams/elf64lriscv-defs.sh: New file.
	* emulparams/elf64lriscv.sh: New file.
	* emultempl/riscvelf.em: New file.

opcodes	* configure.ac: Add entry for bfd_riscv_arch.
	* configure: Regenerate.
	* disassemble.c (disassembler): Add support for riscv.
	(disassembler_usage): Likewise.
	* riscv-dis.c: New file.
	* riscv-opc.c: New file.

include	* dis-asm.h: Add prototypes for print_insn_riscv and
	print_riscv_disassembler_options.
	* elf/riscv.h: New file.
	* opcode/riscv-opc.h: New file.
	* opcode/riscv.h: New file.