arch/arc: fix atomics selection

Due to a kconfig limitation, we can't select a no-prompt symbol that
gets its dependencies by being conditionally re-defined in one or more
if-blocks, like we currently do for BR2_ARCH_HAS_ATOMICS.

As a workaround to this issue, we just redefine that symbol in the arc
if-block, like we do for all other architectures, except that in the arc
case, the default value is conditional.

Reported-by: Anton Kolesov <[email protected]>
[[email protected]: indepently re-done a patch similar to the one
 Thomas made on his own]
Signed-off-by: "Yann E. MORIN" <[email protected]>
Cc: Thomas Petazzoni <[email protected]>
Acked-by: Thomas Petazzoni <[email protected]>
Signed-off-by: Peter Korsgaard <[email protected]>

Author: yann-morin-1998

arch/Config.in.arc

@@ -1,7 +1,9 @@
 # Choise of atomic instructions presence
 config BR2_ARC_ATOMIC_EXT
 	bool "Atomic extension (LLOCK/SCOND instructions)"
-	select BR2_ARCH_HAS_ATOMICS
+
+config BR2_ARCH_HAS_ATOMICS
+	default y if BR2_ARC_ATOMIC_EXT
 
 config BR2_ARCH
 	default "arc"	if BR2_arcle