atomic64_test: simplify the #ifdef for atomic64_dec_if_positive() test

Introduce CONFIG_ARCH_HAS_ATOMIC64_DEC_IF_POSITIVE and use this instead
of the multitude of #if defined() checks in atomic64_test.c

Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Cc: Russell King <linux@arm.linux.org.uk>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Paul Mackerras <paulus@samba.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/arch/s390/Kconfig b/arch/s390/Kconfig
index a39b469..d0a5e92 100644
--- a/arch/s390/Kconfig
+++ b/arch/s390/Kconfig
@@ -85,6 +85,7 @@
 	select HAVE_ARCH_MUTEX_CPU_RELAX
 	select HAVE_ARCH_JUMP_LABEL if !MARCH_G5
 	select ARCH_SAVE_PAGE_KEYS if HIBERNATION
+	select ARCH_HAS_ATOMIC64_DEC_IF_POSITIVE
 	select HAVE_MEMBLOCK
 	select HAVE_MEMBLOCK_NODE_MAP
 	select HAVE_CMPXCHG_LOCAL