target/riscv: refactor Zicond support

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>