RISC-V: Prefetch hint instructions and operand set

RISC-V: Prefetch hint instructions and operand set

This commit adds 'Zicbop' hint instructions.

bfd/ChangeLog:

	* elfxx-riscv.c (riscv_multi_subset_supports): Add handling for
	new instruction class.

gas/ChangeLog:

	* config/tc-riscv.c (riscv_ip): Add handling for new operand
	type 'f' (32-byte aligned pseudo S-type immediate for prefetch
	hints).
	(validate_riscv_insn): Likewise.

include/ChangeLog:

	* opcode/riscv-opc.h (MATCH_PREFETCH_I, MASK_PREFETCH_I,
	MATCH_PREFETCH_R, MASK_PREFETCH_R, MATCH_PREFETCH_W,
	MASK_PREFETCH_W): New macros.
	* opcode/riscv.h (enum riscv_insn_class): Add new instruction
	class INSN_CLASS_ZICBOP.

opcodes/ChangeLog:

	* riscv-dis.c (print_insn_args): Add handling for new operand
	type.
	* riscv-opc.c (riscv_opcodes): Add prefetch hint instructions.