Create a new function serial_max_hds() which returns the number of
serial ports defined by the user. This is needed only by spapr.
This allows us to remove the MAX_SERIAL_PORTS define.
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Tested-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Message-id: 20180420145249.32435-14-peter.maydell@linaro.org