tcg: Widen helper_*_st[bw]_mmu val arguments

tcg: Widen helper_*_st[bw]_mmu val arguments

While the old type was correct in the ideal sense, some ABIs require
the argument to be zero-extended.  Using uint32_t for all such values
is a decent compromise.

Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>