target/riscv: refactor Zicond support

After the original Zicond support was stuck/fell through the cracks on
the mailing list at v3 (and a different implementation was merged in
the meanwhile), we n

target/riscv: refactor Zicond support

After the original Zicond support was stuck/fell through the cracks on
the mailing list at v3 (and a different implementation was merged in
the meanwhile), we need to refactor Zicond to prepare it to be reused
by XVentanaCondOps.

This commit lifts the common logic out into gen_czero and uses this
via gen_logic and 2 helper functions (effectively partial closures).

Reviewed-by: Richard Henderson <richard.henderson@linaro.org>

Signed-off-by: Philipp Tomsich <philipp.tomsich@vrull.eu>
Acked-by: Alistair Francis <alistair.francis@wdc.com>
Message-Id: <20230307180708.302867-2-philipp.tomsich@vrull.eu>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>

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target/riscv: Add support for Zicond extension

The spec can be found in https://github.com/riscv/riscv-zicond.
Two instructions are added:
- czero.eqz: Moves zero to a register rd, if the condition

target/riscv: Add support for Zicond extension

The spec can be found in https://github.com/riscv/riscv-zicond.
Two instructions are added:
- czero.eqz: Moves zero to a register rd, if the condition rs2 is
equal to zero, otherwise moves rs1 to rd.
- czero.nez: Moves zero to a register rd, if the condition rs2 is
nonzero, otherwise moves rs1 to rd.

Signed-off-by: Weiwei Li <liweiwei@iscas.ac.cn>
Signed-off-by: Junqiang Wang <wangjunqiang@iscas.ac.cn>
Reviewed-by: Frank Chang <frank.chang@sifive.com>
Message-ID: <20230221091009.36545-1-liweiwei@iscas.ac.cn>
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>

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