target-info: Add target_riscv64()

target-info: Add target_riscv64()

Adds a helper function to tell if the binary is targeting riscv64 or
not.

Reviewed-by: Pierrick Bouvier <pierrick.bouvier@linaro.org>
Signed-off-by: Anton Johansson <anjo@rev.ng>
Reviewed-by: Chao Liu <chao.liu.zevorn@gmail.com>
Acked-by: Alistair Francis <alistair.francis@wdc.com>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Message-Id: <20260520-hw-riscv-cpu-int-v3-7-d1123ea63d9c@rev.ng>
Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>