sparc: Support atomic64_dec_if_positive properly.

Sparc32 already supported it, as a consequence of using the
generic atomic64 implementation.  And the sparc64 implementation
is rather trivial.

This allows us to set ARCH_HAS_ATOMIC64_DEC_IF_POSITIVE for all
of sparc, and avoid the annoying warning from lib/atomic64_test.c

Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/arch/sparc/Kconfig b/arch/sparc/Kconfig
index b6b442b..9f2edb5 100644
--- a/arch/sparc/Kconfig
+++ b/arch/sparc/Kconfig
@@ -20,6 +20,7 @@
 	select HAVE_ARCH_TRACEHOOK
 	select SYSCTL_EXCEPTION_TRACE
 	select ARCH_WANT_OPTIONAL_GPIOLIB
+	select ARCH_HAS_ATOMIC64_DEC_IF_POSITIVE
 	select RTC_CLASS
 	select RTC_DRV_M48T59
 	select HAVE_IRQ_WORK