target/riscv: Add x-zba, x-zbb, x-zbc and x-zbs properties

target/riscv: Add x-zba, x-zbb, x-zbc and x-zbs properties

The bitmanipulation ISA extensions will be ratified as individual
small extension packages instead of a large B-extension.  The first
new instructions through the door (these have completed public review)
are Zb[abcs].

This adds new 'x-zba', 'x-zbb', 'x-zbc' and 'x-zbs' properties for
these in target/riscv/cpu.[ch].

Signed-off-by: Philipp Tomsich <philipp.tomsich@vrull.eu>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
Message-id: 20210911140016.834071-5-philipp.tomsich@vrull.eu
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>