hw/timer/hpet.c calls address_space_stl_le() declared in
"exec/address-spaces.h". Include it.

This fixes (when modifying unrelated headers):

  hw/timer/hpet.c:210:31: error: use of undeclared identifier 'address_space_memory'
          address_space_stl_le(&address_space_memory, timer->fsb >> 32,
                               ^~~~~~~~~~~~~~~~~~~~

Acked-by: John Snow <jsnow@redhat.com>
Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <20200228114649.12818-12-philmd@redhat.com>
Signed-off-by: Laurent Vivier <laurent@vivier.eu>