UPSTREAM: ARM: 8500/1: fix atags_to_fdt with stack-protector-strong

UPSTREAM: ARM: 8500/1: fix atags_to_fdt with stack-protector-strong

Building with CONFIG_CC_STACKPROTECTOR_STRONG triggers protection code
generation under CONFIG_ARM_ATAG_DTB_COMPAT but this is too early for
being able to use any of the stack_chk code. Explicitly disable it for
only the atags_to_fdt bits.

Change-Id: Ib1f66cc4083b4f04d713c3c70610b8a337a6b0ff
Suggested-by: zhxihu <zhxihu@marvell.com>
Signed-off-by: Kees Cook <keescook@chromium.org>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
Signed-off-by: Frank Wang <frank.wang@rock-chips.com>
(cherry picked from commit 7f66cd3f5420e7d11abd234033e7cb7a9738fc38)