target/riscv/cpu.c: export set_misa()

target/riscv/cpu.c: export set_misa()

We'll move riscv_init_max_cpu_extensions() to tcg-cpu.c in the next
patch and set_misa() needs to be usable from there.

Rename it to riscv_cpu_set_misa() and make it public.

Signed-off-by: Daniel Henrique Barboza <dbarboza@ventanamicro.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Andrew Jones <ajones@ventanamicro.com>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Message-ID: <20230925175709.35696-15-dbarboza@ventanamicro.com>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>