kernel-devsrc: restore compatibility with kernel < v4.10

The kernel commit that added the syscall table generation tools
for ARM platform (ARM: convert to generated system call tables)
wasn't merged until kernel release v4.10.

Current assumption in kernel-devsrc recipe is that these syscall
scripts exist, which breaks the build for external board layers that are
still using 4.9.x kernels:

  cp: cannot stat ‘arch/arm/tools/syscall*’: No such file or directory

so only try to install the scripts when they actually exist.

(From OE-Core rev: 7b4d77d7f909c0ae27553fd9c480f069f12e468f)

Signed-off-by: S. Lockwood-Childs <sjl@vctlabs.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

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

@@ -157,7 +157,12 @@ do_install() {
 	    # include a few files for 'make prepare'
 	    cp -a --parents arch/arm/tools/gen-mach-types $kerneldir/build/
 	    cp -a --parents arch/arm/tools/mach-types $kerneldir/build/
-	    cp -a --parents arch/arm/tools/syscall* $kerneldir/build/
+
+	    # ARM syscall table tools only exist for kernels v4.10 or later
+            SYSCALL_TOOLS=$(find arch/arm/tools -name "syscall*")
+            if [ -n "$SYSCALL_TOOLS" ] ; then
+	        cp -a --parents $SYSCALL_TOOLS $kerneldir/build/
+            fi
 
             cp -a --parents arch/arm/kernel/module.lds $kerneldir/build/
 	fi