target/riscv: reformat @sh format encoding for B-extension

target/riscv: reformat @sh format encoding for B-extension

Signed-off-by: Kito Cheng <[email protected]>
Signed-off-by: Frank Chang <[email protected]>
Reviewed-by: Richard Henderson <[email protected]>
Reviewed-by: Alistair Francis <[email protected]>
Message-id: 20210505160620[email protected]
Signed-off-by: Alistair Francis <[email protected]>