Improve kernel update scripts (#1413)

* Improve kernel update scripts

Use separate script for ODROID-N2 for now. Also warn if there are kernel
patches with a specific kernel version number in the source tree: They
typically can be just moved to the new kernel version, but one should
compile check them before committing.

(cherry picked from commit 96a8ab17c1)

scripts/check-kernel-patches.sh

@@ -0,0 +1,8 @@
+#!/bin/bash
+
+kernel_patches_with_version=$(find buildroot-external -type d -regextype sed -regex ".*/linux/[0-9\.]*")
+
+if [ -n "$kernel_patches_with_version" ]; then
+	echo ""
+	echo "WARNING: Kernel patch directories with kernel version found! Check if updates are needed."
+fi