boards: nrf52_bsim: no-op arm functions as defines

The nrf52 bsim hw models now require some of these to
be defined. For this case we cannot implement these
as static inline functions as that would redefinitions
of the functions.

Signed-off-by: Rubin Gerritsen <rubin.gerritsen@nordicsemi.no>

boards/posix/nrf52_bsim/cmsis.h

@@ -22,10 +22,21 @@ extern "C" {
  * - ARM Instruction Synchronization Barrier
  * - ARM No Operation
  */
-static inline void __DMB(void) {}
-static inline void __DSB(void) {}
-static inline void __ISB(void) {}
-static inline void __NOP(void) {}
+#ifndef __DMB
+#define __DMB()
+#endif
+
+#ifndef __DSB
+#define __DSB()
+#endif
+
+#ifndef __ISB
+#define __ISB()
+#endif
+
+#ifndef __NOP
+#define __NOP()
+#endif
 
 #ifdef __cplusplus
 }