The default number of supported 8250/16550 serial ports is 4, which is not
enough for some platforms. For example, Intel Elkhart Lake CRB has 6 serial
ports in total. Runtime supported ports number can be overridden with the
module parameter "nr_uarts", or boot-time parameter 8250.nr_uarts.

Signed-off-by: Yongxin Liu <yongxin.liu@windriver.com>
Signed-off-by: Bruce Ashfield <bruce.ashfield@gmail.com>