linux-intel: Fix CONFIG_SERIAL_OF_PLATFORM build warning on 5.10

Due to a configuration bug in upstream, the build system outputs a
configuration warning similar to:

---------- CONFIG_SERIAL_OF_PLATFORM -----------------
Config: CONFIG_SERIAL_OF_PLATFORM
From:
[...]/kernel-source/.kernel-meta/configs/v5.10/standard/cfg/8250.cfg
Requested value:  CONFIG_SERIAL_OF_PLATFORM=y
Actual value:

Avoid this by disabling the specific config.

Signed-off-by: Andrei Gherzan <andrei.gherzan@huawei.com>

meta-ohos-staging/recipes-kernel/linux/linux-intel_5.10.bbappend

+# SPDX-FileCopyrightText: Huawei Inc.
+#
+# SPDX-License-Identifier: Apache-2.0
+
+FILESEXTRAPATHS_prepend := "${THISDIR}/linux:"
+
+SRC_URI += "file://misc.cfg"

meta-ohos-staging/recipes-kernel/linux/linux/misc.cfg

+# SPDX-FileCopyrightText: Huawei Inc.
+#
+# SPDX-License-Identifier: Apache-2.0
+
+# Avoid kernel build warnings for x86 nonexitent config
+CONFIG_SERIAL_OF_PLATFORM=n