RISC-V: Cache management instructions

RISC-V: Cache management instructions

This commit adds 'Zicbom' / 'Zicboz' instructions.

bfd/ChangeLog:

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

include/ChangeLog:

	* opcode/riscv-opc.h (MATCH_CBO_CLEAN, MASK_CBO_CLEAN,
	MATCH_CBO_FLUSH, MASK_CBO_FLUSH, MATCH_CBO_INVAL,
	MASK_CBO_INVAL, MATCH_CBO_ZERO, MASK_CBO_ZERO): New macros.
	* opcode/riscv.h (enum riscv_insn_class): Add new instruction
	classes INSN_CLASS_ZICBOM and INSN_CLASS_ZICBOZ.

opcodes/ChangeLog:

	* riscv-opc.c (riscv_opcodes): Add cache-block management
	instructions.