ARM: exynos_defconfig: Enable SECCOMP

Systemd already supports seccomp.  It seems some distros are building
systemd with seccomp, e.g. Arch on ARM, thus leading to boot errors:

systemd-logind.service: Failed at step SECCOMP spawning /usr/lib/systemd/systemd-logind: Invalid argument
Signed-off-by: NKrzysztof Kozlowski <k.kozlowski@samsung.com>
Reviewed-by: NJavier Martinez Canillas <javier@osg.samsung.com>

arch/arm/configs/exynos_defconfig

@@ -17,6 +17,7 @@ CONFIG_PREEMPT=y
 CONFIG_AEABI=y
 CONFIG_HIGHMEM=y
 CONFIG_CMA=y
+CONFIG_SECCOMP=y
 CONFIG_ZBOOT_ROM_TEXT=0x0
 CONFIG_ZBOOT_ROM_BSS=0x0
 CONFIG_ARM_APPENDED_DTB=y