target/riscv: Use 32 bits for misa extensions

target/riscv: Use 32 bits for misa extensions

uint32_t is already in use in most places storing misa extensions such
as CPUArchState::misa_exts, RISCVCPUProfile::misa_exts,
RISCVImpliedExtsRule::implied_misa_exts.  Additionally. the field is
already migrated as uint32_t.

Signed-off-by: Anton Johansson <anjo@rev.ng>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Reviewed-by: Pierrick Bouvier <pierrick.bouvier@linaro.org>
Message-ID: <20251001073306.28573-2-anjo@rev.ng>
Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>