arch: remove no-longer default on atomics option

Now that all architectures explicitly select this option when it makes
sense, there is no need to have a default value.

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Cc: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Cc: Anton Kolesov <Anton.Kolesov@synopsys.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

arch/Config.in

@@ -253,7 +253,6 @@ config BR2_GCC_TARGET_MODE
 # If the architecture has atomic operations, select this:
 config BR2_ARCH_HAS_ATOMICS
 	bool
-	default y if !BR2_arc
 
 # Set up target binary format
 choice