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