kernel-devsrc.bb: Replace extra System.map file with symlink

Currently there are two .map files being copied to $kerneldir/build.
One of the files is System.map and the other is
System.map-<kernel version>. Each .map file takes up about 5MB and
have identical sha256sum hashes. This change will make it so only
System.map-<kernel version> is copied in order to save disk space.
It also recreates System.map as a symlink to that .map file.

(From OE-Core rev: cc971fffb134aa6af9edeabb7a5f4143dee2151e)

Signed-off-by: Erick Shepherd <erick.shepherd@ni.com>
Signed-off-by: Mathieu Dubois-Briand <mathieu.dubois-briand@bootlin.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta/recipes-kernel/linux/kernel-devsrc.bb

@@ -75,7 +75,8 @@ do_install() {
         if [ -s Module.symvers ]; then
             cp Module.symvers $kerneldir/build
         fi
-        cp System.map* $kerneldir/build
+        cp System.map-* $kerneldir/build
+        ln -s System.map-* $kerneldir/build/System.map
         if [ -s Module.markers ]; then
             cp Module.markers $kerneldir/build
         fi