target/xtensa: Set disassemble_info::endian value in disas_set_info()

Have the CPUClass::disas_set_info() callback set the
disassemble_info::endian field.

Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <20250210212931.62401-10-philmd@linaro.org>