RISC-V: Add .insn support.

RISC-V: Add .insn support.

	gas/ChangeLog
	2018-03-07  Kito Cheng  <kito.cheng@gmail.com>
	* config/tc-riscv.c (opcode_name_list): New.
	(opcode_names_hash): Likewise.
	(init_opcode_names_hash): Likewise.
	(opcode_name_lookup): Likewise.
	(validate_riscv_insn): New argument length, and add new format
	which used in .insn directive.
	(md_begin): Refine hash table initialization logic into
	init_opcode_hash.
	(init_opcode_hash): New.
	(my_getOpcodeExpression): Parse opcode name for .insn.
	(riscv_ip): New argument hash, able to handle .insn directive.
	(s_riscv_insn): Handler for .insn directive.
	(riscv_pseudo_table): New entry for .insn.
	* doc/c-riscv.texi: Add documentation for .insn directive.
	* testsuite/gas/riscv/insn.d: Add testcase for .insn directive.
	* testsuite/gas/riscv/insn.s: Likewise.

	include/ChangeLog
	2018-03-07  Kito Cheng  <kito.cheng@gmail.com>
	* opcode/riscv.h (OP_MASK_FUNCT3): New.
	(OP_SH_FUNCT3): Likewise.
	(OP_MASK_FUNCT7): Likewise.
	(OP_SH_FUNCT7): Likewise.
	(OP_MASK_OP2): Likewise.
	(OP_SH_OP2): Likewise.
	(OP_MASK_CFUNCT4): Likewise.
	(OP_SH_CFUNCT4): Likewise.
	(OP_MASK_CFUNCT3): Likewise.
	(OP_SH_CFUNCT3): Likewise.
	(riscv_insn_types): Likewise.

	opcodes/ChangeLog
	2018-03-07  Kito Cheng  <kito.cheng@gmail.com>
	* riscv-opc.c (riscv_insn_types): New.