tcg: Fold deposit with zero to and

Inserting a zero into a value, or inserting a value
into zero at offset 0 may be implemented with AND.

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