RISC-V: Supports Zcb extension.

RISC-V: Supports Zcb extension.

This patch support Zcb extension, contains new compressed instructions,
some instructions depend on other existed extension, like 'zba', 'zbb'
and 'zmmul'.  Zcb also imply Zca extension to enable the compressing
features.

Co-Authored by: Charlie Keaney <charlie.keaney@embecosm.com>
Co-Authored by: Mary Bennett <mary.bennett@embecosm.com>
Co-Authored by: Nandni Jamnadas <nandni.jamnadas@embecosm.com>
Co-Authored by: Sinan Lin <sinan.lin@linux.alibaba.com>
Co-Authored by: Simon Cook <simon.cook@embecosm.com>
Co-Authored by: Shihua Liao <shihua@iscas.ac.cn>
Co-Authored by: Yulong Shi <yulong@iscas.ac.cn>

bfd/ChangeLog:

        * elfxx-riscv.c (riscv_multi_subset_supports): New extension.
        (riscv_multi_subset_supports_ext): Ditto.

gas/ChangeLog:

        * config/tc-riscv.c (validate_riscv_insn): New operators.
        (riscv_ip): Ditto.
        * testsuite/gas/riscv/zcb.d: New test.
        * testsuite/gas/riscv/zcb.s: New test.

include/ChangeLog:

        * opcode/riscv-opc.h (MATCH_C_LBU): New opcode.
        (MASK_C_LBU): New mask.
        (MATCH_C_LHU): New opcode.
        (MASK_C_LHU): New mask.
        (MATCH_C_LH): New opcode.
        (MASK_C_LH): New mask.
        (MATCH_C_SB): New opcode.
        (MASK_C_SB): New mask.
        (MATCH_C_SH): New opcode.
        (MASK_C_SH): New mask.
        (MATCH_C_ZEXT_B): New opcode.
        (MASK_C_ZEXT_B): New mask.
        (MATCH_C_SEXT_B): New opcode.
        (MASK_C_SEXT_B): New mask.
        (MATCH_C_ZEXT_H): New opcode.
        (MASK_C_ZEXT_H): New mask.
        (MATCH_C_SEXT_H): New opcode.
        (MASK_C_SEXT_H): New mask.
        (MATCH_C_ZEXT_W): New opcode.
        (MASK_C_ZEXT_W): New mask.
        (MATCH_C_NOT): New opcode.
        (MASK_C_NOT): New mask.
        (MATCH_C_MUL): New opcode.
        (MASK_C_MUL): New mask.
        (DECLARE_INSN): New opcode.
        * opcode/riscv.h (EXTRACT_ZCB_BYTE_UIMM): New inline func.
        (EXTRACT_ZCB_HALFWORD_UIMM): Ditto.
        (ENCODE_ZCB_BYTE_UIMM): Ditto.
        (ENCODE_ZCB_HALFWORD_UIMM): Ditto.
        (VALID_ZCB_BYTE_UIMM): Ditto.
        (VALID_ZCB_HALFWORD_UIMM): Ditto.
        (enum riscv_insn_class): New extension class.

opcodes/ChangeLog:

        * riscv-dis.c (print_insn_args): New operators.
        * riscv-opc.c: New instructions.