hw/xtensa: Include missing 'exec/tswap.h' header

hw/xtensa: Include missing 'exec/tswap.h' header

Some files indirectly get "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:

  hw/xtensa/bootparam.h:40:16: error: call to undeclared function 'tswap16'; ISO C99 and later do not support implicit function declarations [-Wimplicit-function-declaration]
     40 |         .tag = tswap16(tag),
        |                ^

Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <20241211230357.97036-9-philmd@linaro.org>