accel/tcg: Include missing 'exec/tswap.h' header in translator.c

accel/tcg: Include missing 'exec/tswap.h' header in translator.c

translator.c indirectly gets "exec/tswap.h" declarations via
"exec/cpu-all.h". Include it directly to be able to remove the
former from the latter, otherwise we get:

  accel/tcg/translator.c:433:15: error: call to undeclared function 'tswap16'; ISO C99 and later do not support implicit function declarations [-Wimplicit-function-declaration]
    433 |         tgt = tswap16(raw);
        |               ^

Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <20241211230357.97036-4-philmd@linaro.org>