[arch][arm][cortex-m] select the simplified arch interrupt save/restore for armv6m too
Previously had only selected armv7m for the simplified version.
Forgot that cortex-m0s are armv6m and could use this version.
@@ -50,7 +50,7 @@ static inline void arch_spin_unlock(spin_lock_t *lock) {
#endif
-#if !ARM_ISA_ARMV7M
+#if !(ARM_ISA_ARMV7M || ARM_ISA_ARMV6M)
/* ARM specific flags */
#define SPIN_LOCK_FLAG_IRQ 0x40000000
