tcg: Add flags argument to tcg_gen_bswap16_*, tcg_gen_bswap32_i64

tcg: Add flags argument to tcg_gen_bswap16_*, tcg_gen_bswap32_i64

Implement the new semantics in the fallback expansion.
Change all callers to supply the flags that keep the
semantics unchanged locally.

Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>