tcg/riscv: Rationalize args to tcg_out_qemu_{ld,st}

tcg/riscv: Rationalize args to tcg_out_qemu_{ld,st}

Interpret the variable argument placement in the caller.  Pass data_type
instead of is64 -- there are several places where we already convert back
from bool to type.  Clean things up by using type throughout.

Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Daniel Henrique Barboza <dbarboza@ventanamicro.com>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>