board/arcturus/ppc-ucp1020: add patch to fix build with gcc 6.x.

board/arcturus/ppc-ucp1020: add patch to fix build with gcc 6.x.

This commit adds a Linux kernel patch to solve a build failure with
the arcturus_ucp1020_defconfig with gcc 6.x:

arch/powerpc/kernel/ptrace.c:407:24: warning: index 32 denotes an offset greater than size of 'u64[32][1] {aka long long unsigned int[32][1]}' [-Warray-bounds]
        offsetof(struct thread_fp_state, fpr[32][0]));
                        ^

The patch is upstream in Linux, and can be dropped when
arcturus_ucp1020_defconfig is updated to use a new Linux kernel
version.

Signed-off-by: Oleksandr Zhadan <oleks@arcturusnetworks.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>