bsp/intel-x86: increase maximum number of supported 8250 serial ports to 16

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>

bsp/intel-x86/intel-x86-serial-8250-overrides.cfg

+# SPDX-License-Identifier: MIT
+CONFIG_SERIAL_8250_NR_UARTS=16
+CONFIG_SERIAL_8250_RUNTIME_UARTS=16

bsp/intel-x86/intel-x86.scc

@@ -62,3 +62,4 @@ kconf hardware intel-x86-ixgbe-overrides.cfg
 kconf hardware intel-x86-i915-overrides.cfg
 kconf hardware intel-x86-cfg80211-overrides.cfg
 kconf hardware intel-x86-dptf-overrides.cfg
+kconf hardware intel-x86-serial-8250-overrides.cfg