target/riscv: Restrict riscv_cpu_do_interrupt() to sysemu

target/riscv: Restrict riscv_cpu_do_interrupt() to sysemu

riscv_cpu_do_interrupt() is not reachable on user emulation.

Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Daniel Henrique Barboza <dbarboza@ventanamicro.com>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Message-Id: <20230626232007.8933-7-philmd@linaro.org>